Fixes a multithreading bug in the ruby rpc_server
Fixes a multithreading bug in the ruby rpc_server

This fixes the current ruby server interop test flakiness.

- The interop tests recently changed so that clients access servers in
parallel, meaning that the interop servers handle multiple rpcs at once,
which is how this bug became visible

- since this change, tests run against the ruby interop server have
failed sporadically

- the problem was that the block in #loop_handle_server_calls that is
  passed to the thread pool referenced a var in an enclosing block,
  which resulted in requests being processed by the wrong handler

- this fix ensures that the block to be run on the thread pool thread
  does not have any references to vars in the enclosing block

simonkuang/grpc,kumaralokgithub/grpc,wcevans/grpc,zhimingxie/grpc,thunderboltsid/grpc,kumaralokgithub/grpc,Vizerai/grpc,chrisdunelm/grpc,makdharma/grpc,VcamX/grpc,ncteisen/grpc,jboeuf/grpc,hstefan/grpc,kskalski/grpc,daniel-j-born/grpc,geffzhang/grpc,sreecha/grpc,daniel-j-born/grpc,sreecha/grpc,royalharsh/grpc,thinkerou/grpc,baylabs/grpc,7anner/grpc,arkmaxim/grpc,dgquintas/grpc,quizlet/grpc,LuminateWireless/grpc,dgquintas/grpc,malexzx/grpc,jboeuf/grpc,donnadionne/grpc,dgquintas/grpc,fuchsia-mirror/third_party-grpc,vjpai/grpc,jcanizales/grpc,Vizerai/grpc,perumaalgoog/grpc,thinkerou/grpc,simonkuang/grpc,deepaklukose/grpc,jcanizales/grpc,muxi/grpc,matt-kwong/grpc,vjpai/grpc,msmania/grpc,pmarks-net/grpc,MakMukhi/grpc,podsvirov/grpc,grpc/grpc,geffzhang/grpc,muxi/grpc,tamihiro/grpc,a-veitch/grpc,firebase/grpc,goldenbull/grpc,soltanmm/grpc,nicolasnoble/grpc,madongfly/grpc,Crevil/grpc,perumaalgoog/grpc,maxwell-demon/grpc,Vizerai/grpc,jcanizales/grpc,VcamX/grpc,LuminateWireless/grpc,baylabs/grpc,murgatroid99/grpc,pszemus/grpc,infinit/grpc,carl-mastrangelo/grpc,yang-g/grpc,bogdandrutu/grpc,ejona86/grpc,a11r/grpc,donnadionne/grpc,goldenbull/grpc,tengyifei/grpc,yugui/grpc,carl-mastrangelo/grpc,soltanmm-google/grpc,soltanmm/grpc,a11r/grpc,msmania/grpc,firebase/grpc,madongfly/grpc,yang-g/grpc,dklempner/grpc,Crevil/grpc,soltanmm-google/grpc,MakMukhi/grpc,andrewpollock/grpc,kskalski/grpc,madongfly/grpc,kriswuollett/grpc,jtattermusch/grpc,ctiller/grpc,MakMukhi/grpc,firebase/grpc,grani/grpc,a11r/grpc,mehrdada/grpc,muxi/grpc,leifurhauks/grpc,yongni/grpc,royalharsh/grpc,a-veitch/grpc,muxi/grpc,perumaalgoog/grpc,grani/grpc,geffzhang/grpc,grani/grpc,ipylypiv/grpc,wcevans/grpc,sreecha/grpc,leifurhauks/grpc,y-zeng/grpc,yugui/grpc,PeterFaiman/ruby-grpc-minimal,grpc/grpc,leifurhauks/grpc,stanley-cheung/grpc,msmania/grpc,podsvirov/grpc,quizlet/grpc,jtattermusch/grpc,quizlet/grpc,madongfly/grpc,vjpai/grpc,thunderboltsid/grpc,yang-g/grpc,carl-mastrangelo/grpc,firebase/grpc,ppietrasa/grpc,sreecha/grpc,pmarks-net/grpc,matt-kwong/grpc,deepaklukose/grpc,jboeuf/grpc,simonkuang/grpc,jboeuf/grpc,LuminateWireless/grpc,sreecha/grpc,tengyifei/grpc,arkmaxim/grpc,7anner/grpc,kskalski/grpc,ananthonline/grpc,infinit/grpc,daniel-j-born/grpc,jtattermusch/grpc,simonkuang/grpc,soltanmm/grpc,wcevans/grpc,leifurhauks/grpc,ppietrasa/grpc,matt-kwong/grpc,msiedlarek/grpc,greasypizza/grpc,yang-g/grpc,bogdandrutu/grpc,thinkerou/grpc,maxwell-demon/grpc,kriswuollett/grpc,zhimingxie/grpc,vjpai/grpc,maxwell-demon/grpc,podsvirov/grpc,Vizerai/grpc,donnadionne/grpc,wcevans/grpc,msmania/grpc,kpayson64/grpc,muxi/grpc,fuchsia-mirror/third_party-grpc,donnadionne/grpc,goldenbull/grpc,LuminateWireless/grpc,ppietrasa/grpc,vsco/grpc,ctiller/grpc,grpc/grpc,ipylypiv/grpc,quizlet/grpc,leifurhauks/grpc,vjpai/grpc,ipylypiv/grpc,LuminateWireless/grpc,goldenbull/grpc,dklempner/grpc,PeterFaiman/ruby-grpc-minimal,a11r/grpc,pmarks-net/grpc,philcleveland/grpc,vjpai/grpc,kumaralokgithub/grpc,leifurhauks/grpc,malexzx/grpc,soltanmm-google/grpc,dgquintas/grpc,andrewpollock/grpc,thinkerou/grpc,matt-kwong/grpc,greasypizza/grpc,jboeuf/grpc,deepaklukose/grpc,infinit/grpc,malexzx/grpc,philcleveland/grpc,kpayson64/grpc,w4-sjcho/grpc,a-veitch/grpc,ejona86/grpc,baylabs/grpc,donnadionne/grpc,ipylypiv/grpc,ppietrasa/grpc,ncteisen/grpc,leifurhauks/grpc,pszemus/grpc,baylabs/grpc,jcanizales/grpc,vjpai/grpc,muxi/grpc,simonkuang/grpc,kpayson64/grpc,murgatroid99/grpc,hstefan/grpc,miselin/grpc,grani/grpc,dklempner/grpc,kpayson64/grpc,greasypizza/grpc,madongfly/grpc,mehrdada/grpc,w4-sjcho/grpc,murgatroid99/grpc,andrewpollock/grpc,ctiller/grpc,royalharsh/grpc,makdharma/grpc,fuchsia-mirror/third_party-grpc,rjshade/grpc,firebase/grpc,podsvirov/grpc,w4-sjcho/grpc,kumaralokgithub/grpc,chrisdunelm/grpc,ananthonline/grpc,a11r/grpc,soltanmm/grpc,andrewpollock/grpc,ncteisen/grpc,perumaalgoog/grpc,ncteisen/grpc,LuminateWireless/grpc,ipylypiv/grpc,kumaralokgithub/grpc,jboeuf/grpc,msmania/grpc,wcevans/grpc,carl-mastrangelo/grpc,jtattermusch/grpc,simonkuang/grpc,yongni/grpc,Vizerai/grpc,nicolasnoble/grpc,leifurhauks/grpc,grpc/grpc,adelez/grpc,bogdandrutu/grpc,firebase/grpc,perumaalgoog/grpc,arkmaxim/grpc,dklempner/grpc,pszemus/grpc,msiedlarek/grpc,rjshade/grpc,arkmaxim/grpc,grani/grpc,VcamX/grpc,soltanmm/grpc,nicolasnoble/grpc,jtattermusch/grpc,w4-sjcho/grpc,yang-g/grpc,a-veitch/grpc,tengyifei/grpc,pszemus/grpc,ncteisen/grpc,firebase/grpc,thunderboltsid/grpc,kriswuollett/grpc,thinkerou/grpc,hstefan/grpc,matt-kwong/grpc,mehrdada/grpc,quizlet/grpc,kpayson64/grpc,PeterFaiman/ruby-grpc-minimal,soltanmm/grpc,y-zeng/grpc,kumaralokgithub/grpc,stanley-cheung/grpc,thunderboltsid/grpc,deepaklukose/grpc,hstefan/grpc,y-zeng/grpc,simonkuang/grpc,dgquintas/grpc,quizlet/grpc,arkmaxim/grpc,donnadionne/grpc,yugui/grpc,matt-kwong/grpc,philcleveland/grpc,soltanmm-google/grpc,donnadionne/grpc,zhimingxie/grpc,bogdandrutu/grpc,murgatroid99/grpc,w4-sjcho/grpc,LuminateWireless/grpc,yang-g/grpc,greasypizza/grpc,ppietrasa/grpc,PeterFaiman/ruby-grpc-minimal,stanley-cheung/grpc,PeterFaiman/ruby-grpc-minimal,andrewpollock/grpc,ananthonline/grpc,Crevil/grpc,thunderboltsid/grpc,msiedlarek/grpc,dgquintas/grpc,chrisdunelm/grpc,grani/grpc,simonkuang/grpc,ppietrasa/grpc,w4-sjcho/grpc,bogdandrutu/grpc,dgquintas/grpc,apolcyn/grpc,madongfly/grpc,kskalski/grpc,ananthonline/grpc,yugui/grpc,sreecha/grpc,podsvirov/grpc,chrisdunelm/grpc,chrisdunelm/grpc,muxi/grpc,jboeuf/grpc,deepaklukose/grpc,makdharma/grpc,baylabs/grpc,pszemus/grpc,ncteisen/grpc,ncteisen/grpc,philcleveland/grpc,mehrdada/grpc,vjpai/grpc,ejona86/grpc,vsco/grpc,mehrdada/grpc,makdharma/grpc,ananthonline/grpc,ejona86/grpc,soltanmm/grpc,yugui/grpc,rjshade/grpc,sreecha/grpc,adelez/grpc,geffzhang/grpc,chrisdunelm/grpc,ipylypiv/grpc,Crevil/grpc,a-veitch/grpc,infinit/grpc,PeterFaiman/ruby-grpc-minimal,kpayson64/grpc,mehrdada/grpc,firebase/grpc,malexzx/grpc,rjshade/grpc,Vizerai/grpc,y-zeng/grpc,philcleveland/grpc,a-veitch/grpc,jcanizales/grpc,carl-mastrangelo/grpc,tamihiro/grpc,y-zeng/grpc,dgquintas/grpc,perumaalgoog/grpc,bogdandrutu/grpc,apolcyn/grpc,PeterFaiman/ruby-grpc-minimal,goldenbull/grpc,miselin/grpc,vsco/grpc,ipylypiv/grpc,sreecha/grpc,ncteisen/grpc,tengyifei/grpc,kriswuollett/grpc,donnadionne/grpc,w4-sjcho/grpc,miselin/grpc,w4-sjcho/grpc,stanley-cheung/grpc,wcevans/grpc,greasypizza/grpc,tamihiro/grpc,ctiller/grpc,donnadionne/grpc,kskalski/grpc,kpayson64/grpc,grpc/grpc,stanley-cheung/grpc,infinit/grpc,LuminateWireless/grpc,stanley-cheung/grpc,vsco/grpc,y-zeng/grpc,grani/grpc,soltanmm-google/grpc,chrisdunelm/grpc,malexzx/grpc,muxi/grpc,yongni/grpc,miselin/grpc,tamihiro/grpc,kriswuollett/grpc,7anner/grpc,pszemus/grpc,yugui/grpc,pszemus/grpc,malexzx/grpc,dgquintas/grpc,kskalski/grpc,arkmaxim/grpc,rjshade/grpc,Vizerai/grpc,quizlet/grpc,VcamX/grpc,malexzx/grpc,baylabs/grpc,tengyifei/grpc,ctiller/grpc,donnadionne/grpc,ctiller/grpc,Crevil/grpc,MakMukhi/grpc,carl-mastrangelo/grpc,ananthonline/grpc,a-veitch/grpc,quizlet/grpc,bogdandrutu/grpc,arkmaxim/grpc,royalharsh/grpc,andrewpollock/grpc,adelez/grpc,jboeuf/grpc,kumaralokgithub/grpc,greasypizza/grpc,stanley-cheung/grpc,miselin/grpc,hstefan/grpc,yugui/grpc,kpayson64/grpc,dklempner/grpc,madongfly/grpc,ppietrasa/grpc,baylabs/grpc,daniel-j-born/grpc,ctiller/grpc,podsvirov/grpc,adelez/grpc,adelez/grpc,dklempner/grpc,nicolasnoble/grpc,yongni/grpc,soltanmm-google/grpc,carl-mastrangelo/grpc,msiedlarek/grpc,pszemus/grpc,thunderboltsid/grpc,ctiller/grpc,carl-mastrangelo/grpc,chrisdunelm/grpc,murgatroid99/grpc,yugui/grpc,thunderboltsid/grpc,ncteisen/grpc,murgatroid99/grpc,vjpai/grpc,thunderboltsid/grpc,ananthonline/grpc,ctiller/grpc,goldenbull/grpc,ejona86/grpc,geffzhang/grpc,w4-sjcho/grpc,pmarks-net/grpc,zhimingxie/grpc,ananthonline/grpc,tengyifei/grpc,kriswuollett/grpc,a-veitch/grpc,thinkerou/grpc,MakMukhi/grpc,perumaalgoog/grpc,firebase/grpc,vjpai/grpc,zhimingxie/grpc,vsco/grpc,mehrdada/grpc,MakMukhi/grpc,jcanizales/grpc,podsvirov/grpc,wcevans/grpc,mehrdada/grpc,daniel-j-born/grpc,Vizerai/grpc,y-zeng/grpc,dklempner/grpc,andrewpollock/grpc,royalharsh/grpc,fuchsia-mirror/third_party-grpc,a-veitch/grpc,carl-mastrangelo/grpc,soltanmm/grpc,msmania/grpc,philcleveland/grpc,a11r/grpc,kpayson64/grpc,vsco/grpc,maxwell-demon/grpc,dgquintas/grpc,nicolasnoble/grpc,kskalski/grpc,msiedlarek/grpc,7anner/grpc,stanley-cheung/grpc,infinit/grpc,miselin/grpc,daniel-j-born/grpc,Vizerai/grpc,makdharma/grpc,fuchsia-mirror/third_party-grpc,baylabs/grpc,andrewpollock/grpc,chrisdunelm/grpc,wcevans/grpc,adelez/grpc,carl-mastrangelo/grpc,a11r/grpc,carl-mastrangelo/grpc,perumaalgoog/grpc,ejona86/grpc,apolcyn/grpc,bogdandrutu/grpc,kumaralokgithub/grpc,rjshade/grpc,tamihiro/grpc,stanley-cheung/grpc,ppietrasa/grpc,fuchsia-mirror/third_party-grpc,baylabs/grpc,philcleveland/grpc,firebase/grpc,Vizerai/grpc,ejona86/grpc,maxwell-demon/grpc,tamihiro/grpc,rjshade/grpc,thinkerou/grpc,sreecha/grpc,Crevil/grpc,hstefan/grpc,kpayson64/grpc,malexzx/grpc,VcamX/grpc,madongfly/grpc,nicolasnoble/grpc,VcamX/grpc,nicolasnoble/grpc,apolcyn/grpc,grani/grpc,jtattermusch/grpc,deepaklukose/grpc,nicolasnoble/grpc,pmarks-net/grpc,7anner/grpc,stanley-cheung/grpc,fuchsia-mirror/third_party-grpc,apolcyn/grpc,kpayson64/grpc,Crevil/grpc,tamihiro/grpc,infinit/grpc,Vizerai/grpc,simonkuang/grpc,apolcyn/grpc,zhimingxie/grpc,ctiller/grpc,fuchsia-mirror/third_party-grpc,makdharma/grpc,ipylypiv/grpc,dklempner/grpc,quizlet/grpc,miselin/grpc,ejona86/grpc,thunderboltsid/grpc,dgquintas/grpc,PeterFaiman/ruby-grpc-minimal,infinit/grpc,murgatroid99/grpc,kumaralokgithub/grpc,maxwell-demon/grpc,7anner/grpc,msmania/grpc,nicolasnoble/grpc,kskalski/grpc,geffzhang/grpc,jboeuf/grpc,VcamX/grpc,thinkerou/grpc,vsco/grpc,maxwell-demon/grpc,perumaalgoog/grpc,ctiller/grpc,deepaklukose/grpc,philcleveland/grpc,vsco/grpc,makdharma/grpc,adelez/grpc,hstefan/grpc,muxi/grpc,ncteisen/grpc,goldenbull/grpc,wcevans/grpc,miselin/grpc,jtattermusch/grpc,jcanizales/grpc,pszemus/grpc,hstefan/grpc,pszemus/grpc,matt-kwong/grpc,maxwell-demon/grpc,podsvirov/grpc,nicolasnoble/grpc,zhimingxie/grpc,pszemus/grpc,soltanmm-google/grpc,tamihiro/grpc,royalharsh/grpc,pmarks-net/grpc,carl-mastrangelo/grpc,yongni/grpc,chrisdunelm/grpc,msmania/grpc,tengyifei/grpc,ppietrasa/grpc,msiedlarek/grpc,mehrdada/grpc,kriswuollett/grpc,grpc/grpc,stanley-cheung/grpc,yongni/grpc,zhimingxie/grpc,ctiller/grpc,geffzhang/grpc,tengyifei/grpc,Crevil/grpc,firebase/grpc,sreecha/grpc,goldenbull/grpc,a11r/grpc,VcamX/grpc,LuminateWireless/grpc,ejona86/grpc,madongfly/grpc,vjpai/grpc,daniel-j-born/grpc,makdharma/grpc,soltanmm-google/grpc,podsvirov/grpc,tamihiro/grpc,nicolasnoble/grpc,maxwell-demon/grpc,grpc/grpc,andrewpollock/grpc,vsco/grpc,adelez/grpc,thinkerou/grpc,jboeuf/grpc,MakMukhi/grpc,stanley-cheung/grpc,sreecha/grpc,jboeuf/grpc,msiedlarek/grpc,jcanizales/grpc,MakMukhi/grpc,msmania/grpc,ncteisen/grpc,donnadionne/grpc,apolcyn/grpc,ejona86/grpc,makdharma/grpc,rjshade/grpc,grpc/grpc,thinkerou/grpc,firebase/grpc,royalharsh/grpc,a11r/grpc,zhimingxie/grpc,yang-g/grpc,yugui/grpc,fuchsia-mirror/third_party-grpc,tengyifei/grpc,kriswuollett/grpc,donnadionne/grpc,7anner/grpc,jcanizales/grpc,murgatroid99/grpc,vjpai/grpc,grpc/grpc,greasypizza/grpc,VcamX/grpc,geffzhang/grpc,miselin/grpc,PeterFaiman/ruby-grpc-minimal,arkmaxim/grpc,soltanmm/grpc,apolcyn/grpc,ncteisen/grpc,yongni/grpc,dklempner/grpc,pmarks-net/grpc,msiedlarek/grpc,royalharsh/grpc,goldenbull/grpc,yang-g/grpc,7anner/grpc,PeterFaiman/ruby-grpc-minimal,rjshade/grpc,jtattermusch/grpc,bogdandrutu/grpc,ipylypiv/grpc,mehrdada/grpc,greasypizza/grpc,Crevil/grpc,msiedlarek/grpc,sreecha/grpc,daniel-j-born/grpc,arkmaxim/grpc,royalharsh/grpc,malexzx/grpc,jtattermusch/grpc,matt-kwong/grpc,jboeuf/grpc,chrisdunelm/grpc,pszemus/grpc,jtattermusch/grpc,pmarks-net/grpc,grpc/grpc,jtattermusch/grpc,philcleveland/grpc,deepaklukose/grpc,murgatroid99/grpc,thinkerou/grpc,infinit/grpc,hstefan/grpc,grani/grpc,ejona86/grpc,muxi/grpc,apolcyn/grpc,yongni/grpc,y-zeng/grpc,fuchsia-mirror/third_party-grpc,daniel-j-born/grpc,deepaklukose/grpc,MakMukhi/grpc,adelez/grpc,leifurhauks/grpc,ananthonline/grpc,mehrdada/grpc,kskalski/grpc,y-zeng/grpc,geffzhang/grpc,muxi/grpc,mehrdada/grpc,grpc/grpc,greasypizza/grpc,7anner/grpc,thinkerou/grpc,yongni/grpc,murgatroid99/grpc,grpc/grpc,jtattermusch/grpc,matt-kwong/grpc,nicolasnoble/grpc,muxi/grpc,soltanmm-google/grpc,pmarks-net/grpc,yang-g/grpc,kriswuollett/grpc,ejona86/grpc