Merge pull request moby#4297 from vvoland/fix-mirrors-hostname-0.12

[0.12 backport] util/resolver: Fix insecure mirrors

Author: tonistiigi

util/resolver/resolver.go

@@ -130,9 +130,10 @@ func NewRegistryConfig(m map[string]config.RegistryConfig) docker.RegistryHosts
 
 			var out []docker.RegistryHost
 
-			for _, mirror := range c.Mirrors {
-				h := newMirrorRegistryHost(mirror)
-				hosts, err := fillInsecureOpts(mirror, m[mirror], h)
+			for _, rawMirror := range c.Mirrors {
+				h := newMirrorRegistryHost(rawMirror)
+				mirrorHost := h.Host
+				hosts, err := fillInsecureOpts(mirrorHost, m[mirrorHost], h)
 				if err != nil {
 					return nil, err
 				}