Improve error message on auth_plugin failure
Improve error message on auth_plugin failure

We should include the error always!

Change-Id: I018f554018c66967588dd7da4176066d4848d552

openstack/python-openstacksdk,stackforge/python-openstacksdk,openstack-infra/shade,stackforge/python-openstacksdk,dtroyer/python-openstacksdk,openstack/python-openstacksdk,jsmartin/shade,dtroyer/python-openstacksdk,openstack-infra/shade,jsmartin/shade