Improve messaging on keystone connection issue
Improve messaging on keystone connection issue

When connection could not be establish to keystone, it mostly
caused by misconfiguration. Updating the error message to make
it easier to troubleshooting.

Change-Id: I292838e57474f524f9b2910e6c22648d41006207
Closes-Bug: #1452955

dan1/django_openstack_auth_proto,redhat-openstack/django_openstack_auth,redhat-openstack/django_openstack_auth,dan1/django_openstack_auth_proto