migrate reference github.com/distribution/reference

The "reference" package was moved to a separate module, which was extracted
from https://github.com/distribution/distribution/commit/b9b19409cf458dcb9e1253ff44ba75bd0620faa6

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/image/pull_test.go

@@ -27,7 +27,7 @@ func TestNewPullCommandErrors(t *testing.T) {
 		},
 		{
 			name:          "invalid-name",
-			expectedError: "invalid reference format: repository name must be lowercase",
+			expectedError: "invalid reference format: repository name (library/UPPERCASE_REPO) must be lowercase",
 			args:          []string{"UPPERCASE_REPO"},
 		},
 		{