BlobInfoCacheDir is set incorrectly when copying images

It is not set based on the root image directory, and always
points at the defaults.  This change will get it to follow
filepath.Join(ir.store.GraphRoot(), "cache") set from libpod.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

libpod/image/docker_registry_options.go

@@ -55,6 +55,7 @@ func (o DockerRegistryOptions) GetSystemContext(parent *types.SystemContext, add
 		sc.DockerRegistryUserAgent = parent.DockerRegistryUserAgent
 		sc.OSChoice = parent.OSChoice
 		sc.ArchitectureChoice = parent.ArchitectureChoice
+		sc.BlobInfoCacheDir = parent.BlobInfoCacheDir
 	}
 	return sc
 }