Add .mailmap file

Add .mailmap file with my new prefered email address

Change-Id: I4b0d50a6bcab3cf3c74cdd64d9feed39f4280231
Reviewed-on: https://review.openstack.org/29740
Reviewed-by: Sean Dague <sean@dague.net>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins

.mailmap

@@ -0,0 +1,3 @@
+# Format is:
+# Name <preferred e-mail> <other e-mail >
+Joe Gordon <joe.gordon0@gmail.com> <jogo@cloudscaling.com>