Add a delorean-repo element

This element allows developers to use Yum repositories
generated via the Delorean tool. This is very useful
for testing upstream packages with TripleO element changes.

Change-Id: I290f1adc9631c1350b0cb7ad52b27b6759de05d8

elements/delorean-repo/pkg-map

@@ -0,0 +1,5 @@
+{
+  "default": {
+    "yum_plugin_priorities_package": "yum-plugin-priorities"
+  }
+}