Adding error codes to image package

Signed-off-by: Srini Brahmaroutu <srbrahma@us.ibm.com>

errors/image.go

@@ -0,0 +1,20 @@
+package errors
+
+// This file contains all of the errors that can be generated from the
+// docker/image component.
+
+import (
+	"net/http"
+
+	"github.com/docker/distribution/registry/api/errcode"
+)
+
+var (
+	// ErrorCodeInvalidImageID is generated when image id specified is incorrectly formatted.
+	ErrorCodeInvalidImageID = errcode.Register(errGroup, errcode.ErrorDescriptor{
+		Value:          "INVALIDIMAGEID",
+		Message:        "image ID '%s' is invalid ",
+		Description:    "The specified image id is incorrectly formatted",
+		HTTPStatusCode: http.StatusInternalServerError,
+	})
+)