internal: testutil: add DevZero helper
internal: testutil: add DevZero helper

This helper acts like /dev/zero (outputs \x00 indefinitely) in an
OS-independent fashion. This ensures we don't need to special-case
around Windows in tests that want to open /dev/zero.

Signed-off-by: Aleksa Sarai <a8eb12d32d6ec07cdf737175ec7d4a0f1b4e1ee7@suse.de>

nalind/docker,shishir-a412ed/docker,ibuildthecloud/docker,madhanrm/docker,johnstep/moby-moby,mikebrow/docker,justincormack/docker,PatrickLang/moby,thaJeztah/docker,djs55/docker,pradipd/moby,unclejack/docker,crosbymichael/docker,kolyshkin/moby,nalind/docker,ripcurld0/moby,Mokolea/docker,pradipd/moby,yummypeng/docker,YuPengZTE/docker,AkihiroSuda/docker,kolyshkin/moby,konstruktoid/docker-1,rancher/docker,Ramzec/docker,tonistiigi/docker,rremer/moby,moby/moby,rancher/docker,konstruktoid/docker-upstream,unclejack/docker,ndeloof/docker,scotttlin/docker,AkihiroSuda/docker,mahak/docker,bearstech/moby,ibuildthecloud/docker,duglin/docker,srust/docker,yosifkit/docker,YuPengZTE/docker,jvanz/docker,tophj-ibm/moby,estesp/docker,jlhawn/docker,jwhonce/docker,thaJeztah/docker,yosifkit/docker,SvenDowideit/docker,dmcgowan/docker,jameszhan/docker,trebonian/docker,flavio/docker,johnstep/moby-moby,KarthikNayak/docker,thaJeztah/docker,crosbymichael/docker,Mokolea/docker,rancher/docker,kojiromike/docker,justincormack/docker,johnstep/moby-moby,laijs/moby,moul/docker,SvenDowideit/docker,dims/docker,yosifkit/docker,ripcurld0/moby,whuwxl/docker,x1022as/docker,jthelin/docker,vdemeester/docker,konstruktoid/docker-1,noironetworks/docker,SvenDowideit/docker,bearstech/moby,nalind/docker,gnailuy/docker,jvanz/docker,konstruktoid/docker-upstream,tophj-ibm/docker,madhanrm/docker,cpuguy83/docker,gnailuy/docker,moul/docker,Ramzec/docker,flavio/docker,tmp6154/docker,jameszhan/docker,scotttlin/docker,ibuildthecloud/docker,moby/moby,x1022as/docker,Mokolea/docker,konstruktoid/docker-upstream,nawawi/docker,noironetworks/docker,kolyshkin/moby,allencloud/docker,rhatdan/docker,laijs/moby,mixja/docker,justincormack/docker,jameszhan/docker,ripcurld0/moby,jimjag/docker,scotttlin/docker,jthelin/docker,yosifkit/docker,djs55/docker,dmcgowan/docker,unclejack/docker,cpuguy83/docker,jimjag/docker,jimjag/docker,rhatdan/docker,rhatdan/docker,paralin/docker,PatrickLang/moby,cpuguy83/docker,Ramzec/docker,rremer/moby,shishir-a412ed/docker,KingEmet/docker,KingEmet/docker,AkihiroSuda/docker,allencloud/docker,Ramzec/docker,tophj-ibm/docker,jwhonce/docker,dccurtis/docker,thaJeztah/docker,laijs/docker,tophj-ibm/moby,moul/docker,jlhawn/docker,dims/docker,srust/docker,Mokolea/docker,docker/docker,tmp6154/docker,mahak/docker,vdemeester/docker,maxamillion/docker,djs55/docker,tmp6154/docker,noironetworks/docker,tophj-ibm/moby,kolyshkin/docker,ibuildthecloud/docker,dmcgowan/docker,maxamillion/docker,konstruktoid/docker-1,yongtang/docker,duglin/docker,vdemeester/docker,nawawi/docker,YuPengZTE/docker,ndeloof/docker,tophj-ibm/docker,jimjag/docker,bearstech/moby,shishir-a412ed/docker,laijs/moby,whuwxl/docker,flavio/docker,duglin/docker,trebonian/docker,x1022as/docker,nawawi/docker,mixja/docker,mikebrow/docker,paralin/docker,madhanrm/docker,ndeloof/docker,PatrickLang/moby,dims/docker,yongtang/docker,moul/docker,yummypeng/docker,konstruktoid/docker-upstream,whuwxl/docker,paralin/docker,cpuguy83/docker,bearstech/moby,srust/docker,jlhawn/docker,mahak/docker,nalind/docker,flavio/docker,moby/moby,KarthikNayak/docker,mikebrow/docker,trebonian/docker,dccurtis/docker,tonistiigi/docker,rremer/moby,nawawi/docker,gnailuy/docker,estesp/docker,mixja/docker,kojiromike/docker,kojiromike/docker,yummypeng/docker,docker/docker,moby/moby,KingEmet/docker,trebonian/docker,gnailuy/docker,laijs/docker,dccurtis/docker,KarthikNayak/docker,allencloud/docker,laijs/docker,mahak/docker,paralin/docker,AkihiroSuda/docker,estesp/docker,yongtang/docker,jvanz/docker,pradipd/moby,docker/docker,tonistiigi/docker,maxamillion/docker,kolyshkin/docker,jwhonce/docker,ibuildthecloud/docker,crosbymichael/docker