Fix go-vet issue
Fix go-vet issue

This fix fixes the following issue with `go vet`:
```
$ go tool vet cmd/dockerd/daemon.go
cmd/dockerd/daemon.go:163: the cancel function is not used on all paths (possible context leak)
cmd/dockerd/daemon.go:167: this return statement may be reached without using the cancel var defined on line 163
```

Signed-off-by: Yong Tang <765086fe2e0c1f980161f127fec596800f327f62@outlook.com>

nawawi/docker,flavio/docker,unclejack/docker,trebonian/docker,pradipd/moby,docker/docker,nalind/docker,Mokolea/docker,yosifkit/docker,moul/docker,dims/docker,thaJeztah/docker,paralin/docker,konstruktoid/docker-1,crosbymichael/docker,djs55/docker,Ramzec/docker,nawawi/docker,bearstech/moby,jwhonce/docker,mahak/docker,kojiromike/docker,kolyshkin/moby,rremer/moby,yongtang/docker,dims/docker,nalind/docker,konstruktoid/docker-1,vdemeester/docker,vdemeester/docker,justincormack/docker,vdemeester/docker,scotttlin/docker,thaJeztah/docker,Ramzec/docker,cpuguy83/docker,cpuguy83/docker,jimjag/docker,nawawi/docker,AkihiroSuda/docker,docker/docker,konstruktoid/docker-1,gnailuy/docker,flavio/docker,pradipd/moby,Mokolea/docker,nalind/docker,cpuguy83/docker,moul/docker,mikebrow/docker,jameszhan/docker,moby/moby,kojiromike/docker,jlhawn/docker,kolyshkin/moby,jthelin/docker,SvenDowideit/docker,justincormack/docker,scotttlin/docker,flavio/docker,jwhonce/docker,kolyshkin/moby,paralin/docker,AkihiroSuda/docker,ibuildthecloud/docker,yosifkit/docker,paralin/docker,unclejack/docker,jameszhan/docker,rremer/moby,konstruktoid/docker-upstream,Mokolea/docker,jameszhan/docker,tmp6154/docker,jlhawn/docker,bearstech/moby,Ramzec/docker,ibuildthecloud/docker,mikebrow/docker,trebonian/docker,jimjag/docker,jimjag/docker,nawawi/docker,moul/docker,mahak/docker,crosbymichael/docker,jimjag/docker,estesp/docker,moul/docker,gnailuy/docker,Ramzec/docker,konstruktoid/docker-upstream,thaJeztah/docker,dims/docker,djs55/docker,trebonian/docker,tmp6154/docker,bearstech/moby,AkihiroSuda/docker,mikebrow/docker,SvenDowideit/docker,yosifkit/docker,jlhawn/docker,estesp/docker,gnailuy/docker,jvanz/docker,flavio/docker,jwhonce/docker,docker/docker,cpuguy83/docker,unclejack/docker,gnailuy/docker,tmp6154/docker,scotttlin/docker,nalind/docker,moby/moby,SvenDowideit/docker,trebonian/docker,konstruktoid/docker-upstream,mahak/docker,AkihiroSuda/docker,ibuildthecloud/docker,bearstech/moby,justincormack/docker,crosbymichael/docker,rremer/moby,jvanz/docker,thaJeztah/docker,moby/moby,jthelin/docker,ibuildthecloud/docker,estesp/docker,mahak/docker,yosifkit/docker,pradipd/moby,ibuildthecloud/docker,jvanz/docker,moby/moby,yongtang/docker,kojiromike/docker,paralin/docker,Mokolea/docker,yongtang/docker,djs55/docker,konstruktoid/docker-upstream