Add unit test for func in remotes/docker/handler.go
Add unit test for func in remotes/docker/handler.go

Signed-off-by: Hu Shuai <a4797ccdc3c71d8ffc5c17a5bb7f114e3818f278@cn.fujitsu.com>

estesp/containerd,mikebrow/containerd,vdemeester/containerd,vdemeester/containerd,dmcgowan/containerd,containerd/containerd,mikebrow/containerd,thaJeztah/containerd,estesp/containerd,containerd/containerd,dmcgowan/containerd,thaJeztah/containerd,crosbymichael/containerd,crosbymichael/containerd