Skip V2 registry and immediately fallback to V1 when mirrors are provided

Since V2 registry does not yet implement mirrors, when mirrors are given automatically fallback to V1 without checking V2 first.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

graph/pull.go

@@ -139,7 +139,7 @@ func (s *TagStore) CmdPull(job *engine.Job) engine.Status {
 		mirrors = s.mirrors
 	}
 
-	if isOfficial || endpoint.Version == registry.APIVersion2 {
+	if len(mirrors) == 0 && (isOfficial || endpoint.Version == registry.APIVersion2) {
 		j := job.Eng.Job("trust_update_base")
 		if err = j.Run(); err != nil {
 			return job.Errorf("error updating trust base graph: %s", err)