[Client] Fix possible goroutine leak.
[Client] Fix possible goroutine leak.

Running goroutines with pullLayer are blocked to send error of a
pull operation. If we abort pulling without notify them about
cancelation they will get stucked forever. To avoid this possible
leak cancelCh was introduced. In case of abort we close that channel
to notify other goroutines about cancelation.

mattmoor/distribution,menglingwei/denverdino.github.io,imranraja85/distribution,BSWANG/denverdino.github.io,sanscontext/docker.github.io,denverdino/docker.github.io,aduermael/docker.github.io,paulczar/distribution,sanscontext/docker.github.io,zerosign/distribution,tdooner/distribution,johnstep/docker.github.io,jpoler/distribution,atyenoria/distribution,denverdino/docker.github.io,aduermael/docker.github.io,yuwaMSFT2/distribution,gorcz/distribution,jrjang/distribution,dobril-stanga/distribution,higebu/distribution,dmcgowan/distribution,londoncalling/docker.github.io,mattmoor/distribution,runcom/distribution,joeuo/docker.github.io,RichardScothern/distribution,aprajshekhar/distribution,calavera/distribution,wangmingshuai/distribution,lcarstensen/distribution,BSWANG/denverdino.github.io,arneluehrs/distribution,CodeJuan/distribution,BSWANG/denverdino.github.io,xiekeyang/distribution,docker-zh/docker.github.io,miminar/distribution,deis/distribution,anweiss/docker.github.io,wking/docker-distribution,phiroict/docker,johnstep/docker.github.io,thaJeztah/distribution,denverdino/denverdino.github.io,zhaytee/distribution,LuisBosquez/docker.github.io,konnase/distribution,manoj535/distribution,CodeJuan/distribution,hopkings2008/distribution,BradleyA/distribution,bdwill/docker.github.io,docker-zh/docker.github.io,bdwill/docker.github.io,lcarstensen/distribution,gavioto/distribution,aaronlehmann/distribution,stevvooe/docker-registry,ChenLingPeng/distribution,curtiszimmerman/distribution,stevvooe/docker-registry,rillig/docker.github.io,gdevillele/docker.github.io,bdwill/docker.github.io,uptownhr/distribution,dalanlan/distribution,mbentley/distribution,bsmr-docker/distribution,danix800/docker.github.io,shin-/docker.github.io,docker/docker.github.io,avinson/distribution,arneluehrs/distribution,troy0820/docker.github.io,docker/docker.github.io,paulczar/distribution,convox/distribution,aybabtme/distribution,stevvooe/distribution,lorieri/distribution,vdemeester/distribution,gdevillele/docker.github.io,denverdino/distribution-fuse,zhangcoldwater/distribution,LuisBosquez/docker.github.io,LuisBosquez/docker.github.io,qiniu/distribution,aduermael/docker.github.io,phiroict/docker,ContainerSolutions/distribution,sebrandon1/distribution,jlhawn/distribution,johnstep/docker.github.io,huamai-io/distribution,mattrgreen/distribution,Tiesheng/distribution,alexisbellido/docker.github.io,adambrett-forks/distribution,shin-/docker.github.io,duglin/distribution,harche/distribution,yuwaMSFT2/distribution,BrianBland/distribution,mikebrow/distribution,duglin/distribution,cyli/distribution,djenriquez/distribution,linearregression/distribution,londoncalling/docker.github.io,zerosign/distribution,orivej/distribution,sergeyfd/distribution,armbuilds/distribution,jzwlqx/denverdino.github.io,rodacom/docker-hub,BrickXu/distribution,AoJ/distribution,joaofnfernandes/docker.github.io,baloo/distribution,tianon/docker-distribution,anweiss/docker.github.io,JimGalasyn/docker.github.io,gdevillele/docker.github.io,menglingwei/denverdino.github.io,jmitchell/distribution,imranraja85/distribution,sergeyfd/distribution,thaJeztah/docker.github.io,LuisBosquez/docker.github.io,JimGalasyn/docker.github.io,phiroict/docker,denverdino/denverdino.github.io,konnase/distribution,ibuildthecloud/distribution,beni55/distribution,rbarlow/distribution,denverdino/docker.github.io,danix800/docker.github.io,anweiss/docker.github.io,Gobliip/distribution,Gobliip/distribution,beni55/distribution,adambrett-forks/distribution,noxiouz/distribution,gdevillele/docker.github.io,mboersma/distribution,bdwill/docker.github.io,joaofnfernandes/docker.github.io,dv/distribution,Seb-Solon/distribution,docker/distribution,jmitchell/distribution,rillig/docker.github.io,jwhonce/distribution,maquanyi/distribution,rochacon/distribution,mikebrow/distribution,djenriquez/distribution,londoncalling/docker.github.io,jzwlqx/denverdino.github.io,denverdino/docker.github.io,amitshukla/distribution,aduermael/docker.github.io,pdevine/distribution,jordimassaguerpla/distribution,RyanDeng/distribution,shin-/docker.github.io,icecrime/distribution,dtromb/distribution,sadlil/distribution,joeuo/docker.github.io,sanscontext/docker.github.io,docker/distribution,johnstep/docker.github.io,aaronlehmann/distribution,wking/docker-distribution,miminar/distribution,zhangcoldwater/distribution,docker/docker.github.io,harrisonfeng/distribution,apuigsech/distribution,BradleyA/distribution,BSWANG/denverdino.github.io,johnstep/docker.github.io,londoncalling/docker.github.io,dv/distribution,AndreyKostov/distribution,iskradelta/distribution,hpcloud/distribution,shakamunyi/distribution,jpoler/distribution,dave-tucker/distribution,jzwlqx/distribution,mattrgreen/distribution,aybabtme/distribution,shakamunyi/distribution,jzwlqx/denverdino.github.io,rochacon/distribution,liubin/distribution,anweiss/docker.github.io,LouisKottmann/distribution,jlhawn/distribution,schu/distribution,spacexnice/distribution,jramseye/distribution,sanscontext/docker.github.io,jzwlqx/denverdino.github.io,tianon/docker-distribution,donhcd/distribution,joaofnfernandes/docker.github.io,dmcgowan/distribution,alexisbellido/docker.github.io,thaJeztah/docker.github.io,tt/distribution,lebauce/distribution,denverdino/docker.github.io,jramseye/distribution,denverdino/denverdino.github.io,13W/distribution,sallyom/distribution,donhcd/distribution,stevvooe/distribution,zhaytee/distribution,jackpgriffin/distribution,humble00/distribution,RichardScothern/distribution,avinson/distribution,tt/distribution,championv/distribution,hanleys/distribution,harrisonfeng/distribution,menglingwei/denverdino.github.io,alexisbellido/docker.github.io,convox/distribution,orivej/distribution,bigsurge/distribution,jonboulle/distribution,iskradelta/distribution,irachex/distribution,rillig/docker.github.io,gorcz/distribution,lindenlab/distribution,jzwlqx/denverdino.github.io,GerritForge/docker-registry,joaofnfernandes/docker.github.io,calavera/distribution,docker/docker.github.io,RaviTezu/distribution,whyrusleeping/distribution,phiroict/docker,shin-/docker.github.io,mboersma/distribution,ibuildthecloud/distribution,moxiegirl/distribution,troy0820/docker.github.io,docker-zh/docker.github.io,tian-xiaobo/distribution,rbarlow/distribution,sanscontext/docker.github.io,cezarsa/distribution,pdevine/distribution,thaJeztah/distribution,higebu/distribution,tian-xiaobo/distribution,curtiszimmerman/distribution,uptownhr/distribution,BSWANG/denverdino.github.io,denverdino/distribution-stevvooe,rodacom/docker-hub,alexisbellido/docker.github.io,denverdino/denverdino.github.io,armbuilds/distribution,dmp42/distribution,anweiss/docker.github.io,codefresh-io/cf-distribution,konstruktoid/distribution,shubheksha/docker.github.io,bsmr-docker/distribution,BrickXu/distribution,13W/distribution,hanleys/distribution,jzwlqx/distribution,joeuo/docker.github.io,troy0820/docker.github.io,sthapaun/distribution,nateww/distribution,phiroict/docker,Seb-Solon/distribution,icecrime/distribution,yeghishe/distribution,endophage/distribution,ChenLingPeng/distribution,humble00/distribution,LuisBosquez/docker.github.io,joeuo/docker.github.io,londoncalling/docker.github.io,konstruktoid/distribution,linearregression/distribution,apuigsech/distribution,wangmingshuai/distribution,BrianBland/distribution,AndreyKostov/distribution,gdevillele/docker.github.io,docker/docker.github.io,Tiesheng/distribution,denverdino/distribution,dalanlan/distribution,denverdino/distribution-fuse,lorieri/distribution,huamai-io/distribution,endophage/distribution,kmala/distribution,cezarsa/distribution,denverdino/distribution,andrewnguyen/distribution,liubin/distribution,JimGalasyn/docker.github.io,thelinuxkid/distribution,RyanDeng/distribution,denverdino/denverdino.github.io,whyrusleeping/distribution,bdwill/docker.github.io,arvindkandhare/distribution,dave-tucker/distribution,AoJ/distribution,moxiegirl/distribution,troy0820/docker.github.io,alexisbellido/docker.github.io,danix800/docker.github.io,bpradipt/distribution,docker-zh/docker.github.io,shubheksha/docker.github.io,shin-/docker.github.io,yeghishe/distribution,schu/distribution,genedock/distribution,RaviTezu/distribution,qiniu/distribution,gierschv/distribution,bobphill/distribution,bxy09/distribution,tschoots/distribution,jhicks-camgian/distribution,denverdino/distribution-stevvooe,sebrandon1/distribution,dmp42/distribution,championv/distribution,amitshukla/distribution,JimGalasyn/docker.github.io,shubheksha/docker.github.io,LouisKottmann/distribution,gavioto/distribution,menglingwei/denverdino.github.io,lindenlab/distribution,mbentley/distribution,deis/distribution,dobril-stanga/distribution,irachex/distribution,thaJeztah/docker.github.io,spacexnice/distribution,aibaars/distribution,danix800/docker.github.io,menglingwei/denverdino.github.io,sthapaun/distribution,dtromb/distribution,andrewnguyen/distribution,thaJeztah/docker.github.io,kmala/distribution,joaofnfernandes/docker.github.io,atyenoria/distribution,noxiouz/distribution,nevermosby/distribution,n1tr0g/distribution,docker-zh/docker.github.io,baloo/distribution,joeuo/docker.github.io,jackpgriffin/distribution,arvindkandhare/distribution,bigsurge/distribution,nwt/distribution,estesp/distribution,bobphill/distribution,bxy09/distribution,tdooner/distribution,n1tr0g/distribution,vdemeester/distribution,jhicks-camgian/distribution,shyr/distribution,aprajshekhar/distribution,aibaars/distribution,xiekeyang/distribution,gierschv/distribution,nevermosby/distribution,GerritForge/docker-registry,jordimassaguerpla/distribution,thaJeztah/docker.github.io,runcom/distribution,thelinuxkid/distribution,rhoml/distribution,shyr/distribution,JimGalasyn/docker.github.io,manoj535/distribution,lebauce/distribution,nwt/distribution,jonboulle/distribution,genedock/distribution,hpcloud/distribution,nateww/distribution,sallyom/distribution,hopkings2008/distribution,tschoots/distribution,rhoml/distribution,sadlil/distribution,codefresh-io/cf-distribution,ContainerSolutions/distribution,shubheksha/docker.github.io,jrjang/distribution,harche/distribution,cyli/distribution,shubheksha/docker.github.io,bpradipt/distribution,rillig/docker.github.io,maquanyi/distribution,estesp/distribution,jwhonce/distribution