Use default user SSH credentials

Use default user SSH credentials rather than forcing the
'releasestatus' user and creds in ~/.gerritssh. This allows
to run locally with your own credentials for testing.

Change-Id: I497f338197cb5ba6c39aa0e5d8b001382ea1f3f5
Reviewed-on: https://review.openstack.org/30882
Approved: Thierry Carrez <thierry@openstack.org>
Reviewed-by: Thierry Carrez <thierry@openstack.org>
Tested-by: Jenkins