Support attaching to containers in forward backend
Support attaching to containers in forward backend

Signed-off-by: Ben Firshman <73675debcd8a436be48ec22211dcf44fe0df0a64@firshman.co.uk>

pssahi/swarm,doronp/swarm,anweiss/docker.github.io,vlajos/swarm,JimGalasyn/docker.github.io,gradywang/swarm,jay-lau/swarm,ezrasilvera/swarm,sfsmithcha/swarm,rajdeepd/swarm,thaJeztah/docker.github.io,rancher/swarm,jeffjen/swarm,bpradipt/swarm,joeuo/docker.github.io,denverdino/docker.github.io,christophelec/swarm,therealbill/swarm,BSWANG/denverdino.github.io,barais/swarm,gdevillele/docker.github.io,danix800/docker.github.io,aluzzardi/swarm,JimGalasyn/docker.github.io,adouang/swarm,errordeveloper/swarm,liubin/swarm,joeuo/docker.github.io,rutulpatel/swarm,abronan/swarm,bsmr-docker/swarm,docker-zh/docker.github.io,londoncalling/docker.github.io,NunoEdgarGub1/swarm,JimGalasyn/docker.github.io,linecheng/swarm,johnstep/docker.github.io,bdwill/docker.github.io,Aorjoa/swarm,BSWANG/denverdino.github.io,troy0820/docker.github.io,tangkun75/swarm,jzwlqx/denverdino.github.io,megamsys/swarm,thaJeztah/docker.github.io,londoncalling/docker.github.io,NunoEdgarGub1/swarm,denverdino/swarm,denverdino/denverdino.github.io,mountkin/swarm,schmunk42/swarm,bsmr-docker/swarm,jdamick/swarm,rillig/docker.github.io,ejholmes/swarm,pdevine/swarm,MHBauer/swarm,jeffjen/swarm,menglingwei/denverdino.github.io,denverdino/denverdino.github.io,swarm-hooks/swarm,mgoelzer/swarm,joaofnfernandes/docker.github.io,swarm-hooks/swarm,shubheksha/docker.github.io,marsmensch/swarm,resouer/swarm,riuvshin/swarm,SivagnanamCiena/swarm,LukasBacigal/swarm,shot/swarm,CiaranCostello/swarm,parapsyche/swarm,mountkin/swarm,troy0820/docker.github.io,iaintshine/swarm,phiroict/docker,FreedomWangLi/swarm,BSWANG/denverdino.github.io,srikalyan/swarm,shin-/docker.github.io,snrism/swarm,denverdino/denverdino.github.io,denverdino/swarm-1,shakamunyi/swarm,atlassian/swarm,danix800/docker.github.io,ricca742/swarm,anweiss/docker.github.io,menglingwei/denverdino.github.io,sanscontext/docker.github.io,docker/docker.github.io,anweiss/docker.github.io,auzias/swarm,tangkun75/swarm,everett-toews/swarm,jzwlqx/denverdino.github.io,LukasBacigal/swarm,vieux/swarm,gonkulator/swarm,cgvarela/swarm,alexisbellido/docker.github.io,rav121/swarm,jzwlqx/denverdino.github.io,shin-/docker.github.io,kyhavlov/swarm,abronan/swarm,phiroict/docker,menglingwei/denverdino.github.io,francisbouvier/swarm,johnstep/docker.github.io,jimmycmh/swarm,joaofnfernandes/docker.github.io,tranceitionalMynd/swarm,rillig/docker.github.io,Spritekin/swarm,gdevillele/docker.github.io,rajdeepd/swarm,LuisBosquez/docker.github.io,docker/docker.github.io,BSWANG/swarm,mgoelzer/swarm,alexisbellido/docker.github.io,mrjana/swarm,bdwill/docker.github.io,EderRoger/swarm,LuisBosquez/docker.github.io,JimGalasyn/docker.github.io,jdamick/swarm,moxiegirl/swarm,johnstep/docker.github.io,affo/swarm,sanscontext/docker.github.io,troy0820/docker.github.io,docker/docker.github.io,doronp/swarm,affo/swarm,bdwill/docker.github.io,shot/swarm,phiroict/docker,sfsmithcha/swarm,ch3lo/swarm,jimmyxian/swarm,ricca742/swarm,krystism/swarm,iaintshine/swarm,Aorjoa/swarm,jimmyxian/swarm,rchicoli/swarm,menglingwei/denverdino.github.io,u2mejc/swarm,anweiss/docker.github.io,ealang/swarm,fugr/swarm,xFragger/swarm,zkcrescent/swarm,qianzhangxa/swarm,rancher/swarm,raoofm/swarm,riuvshin/swarm,FreedomWangLi/swarm,troy0820/docker.github.io,BSWANG/swarm,MHBauer/swarm,errordeveloper/swarm,CiaranCostello/swarm,EderRoger/swarm,aduermael/docker.github.io,qianzhangxa/swarm,aidora/pisces,morpheyesh/swarm,thaJeztah/docker.github.io,allencloud/swarm,sanscontext/docker.github.io,fugr/swarm,shubheksha/docker.github.io,bpradipt/swarm,krystism/swarm,LuisBosquez/docker.github.io,chanwit/swarm,joeuo/docker.github.io,deis/swarm,megamsys/swarm,gdevillele/docker.github.io,danix800/docker.github.io,deis/swarm,bdwill/docker.github.io,joeuo/docker.github.io,jimmycmh/swarm,joaofnfernandes/docker.github.io,rav121/swarm,shakamunyi/swarm,bdwill/docker.github.io,adouang/swarm,PeoplePerHour/libswarm,alexisbellido/docker.github.io,echupriyanov/swarm,docker-zh/docker.github.io,ezrasilvera/SwarmACLs,u2mejc/swarm,beni55/swarm-1,BSWANG/denverdino.github.io,kunalkushwaha/swarm,docker-zh/docker.github.io,vieux/swarm,LuisBosquez/docker.github.io,cgvarela/swarm,jimenez/swarm,denverdino/denverdino.github.io,tranceitionalMynd/swarm,snrism/swarm,danix800/docker.github.io,dnephin/swarm,yp-engineering/swarm,denverdino/docker.github.io,christophelec/swarm,JimGalasyn/docker.github.io,PeoplePerHour/libswarm,allencloud/swarm,rillig/docker.github.io,mrjana/swarm,morpheyesh/swarm,denverdino/docker.github.io,akerbis/armhf-swarm,liubin/swarm,thaJeztah/docker.github.io,ealang/swarm,everett-toews/swarm,denverdino/denverdino.github.io,gonkulator/swarm,linecheng/swarm,ch3lo/swarm,jay-lau/swarm,sanscontext/docker.github.io,chanwit/swarm,rchicoli/swarm,aduermael/docker.github.io,FollowMyDev/swarm,rillig/docker.github.io,tnachen/swarm,akerbis/armhf-swarm,shubheksha/docker.github.io,shin-/docker.github.io,docker/docker.github.io,docker/docker.github.io,phiroict/docker,ezrasilvera/SwarmACLs,joaofnfernandes/docker.github.io,shubheksha/docker.github.io,gradywang/swarm,therealbill/swarm,francisbouvier/swarm,aluzzardi/swarm,vlajos/swarm,johnstep/docker.github.io,alexisbellido/docker.github.io,SivagnanamCiena/swarm,joeuo/docker.github.io,barais/swarm,echupriyanov/swarm,phiroict/docker,kunalkushwaha/swarm,menglingwei/denverdino.github.io,gdevillele/docker.github.io,resouer/swarm,sanscontext/docker.github.io,londoncalling/docker.github.io,atlassian/swarm,raoofm/swarm,zkcrescent/swarm,bfirsh/swarm,mavenugo/swarm,denverdino/docker.github.io,shin-/docker.github.io,shubheksha/docker.github.io,Spritekin/swarm,aduermael/docker.github.io,shin-/docker.github.io,docker-zh/docker.github.io,jzwlqx/denverdino.github.io,unodba/swarm,londoncalling/docker.github.io,joaofnfernandes/docker.github.io,beni55/swarm-1,pssahi/swarm,pdevine/swarm,thaJeztah/docker.github.io,docker-zh/docker.github.io,aduermael/docker.github.io,anweiss/docker.github.io,dims/swarm,CodeNow/swarm,jzwlqx/denverdino.github.io,schmunk42/swarm,parapsyche/swarm,xFragger/swarm,aidora/pisces,ejholmes/swarm,alexisbellido/docker.github.io,dims/swarm,dnephin/swarm,ezrasilvera/swarm,unodba/swarm,polyverse-security/swarm,CodeNow/swarm,cpuguy83/swarm,rutulpatel/swarm,denverdino/swarm-1,shahankhatch/swarm,johnstep/docker.github.io,polyverse-security/swarm,denverdino/swarm,ehazlett/swarm,LuisBosquez/docker.github.io,londoncalling/docker.github.io,yp-engineering/swarm,marsmensch/swarm,gdevillele/docker.github.io,denverdino/docker.github.io,auzias/swarm,ehazlett/swarm,tnachen/swarm,FollowMyDev/swarm,BSWANG/denverdino.github.io,shahankhatch/swarm,kyhavlov/swarm,srikalyan/swarm,moxiegirl/swarm,bfirsh/swarm,cpuguy83/swarm,jimenez/swarm,mavenugo/swarm