Add Docker resolver tests
Add Docker resolver tests

Tests resolving, fetching, and using the various authentication
methods supported by the Docker registry protocol.

Signed-off-by: Derek McGowan <e1c79a582b6629e6b39e9679f4bb964d25db4aa8@mcgstyle.net>

vdemeester/containerd,vdemeester/containerd,containerd/containerd,estesp/containerd,yuexiao-wang/containerd,dmcgowan/containerd,docker/containerd,hqhq/containerd,chanezon/containerd,crosbymichael/containerd,mikebrow/containerd,estesp/containerd,thaJeztah/containerd,miaoyq/containerd,thaJeztah/containerd,lichao-mobanche/containerd,kunalkushwaha/containerd,kunalkushwaha/containerd,containerd/containerd,crosbymichael/containerd,mikebrow/containerd,rajasec/containerd,miaoyq/containerd,AkihiroSuda/containerd,dmcgowan/containerd,xiekeyang/containerd