Fixes test_images_member_rbac missing os credentials for image v2.

Currently Patrole test in image.v2.test_images_member_rbac fails
because of an AttributeError [0], related to the attribute 'os'
missing, meaning that the credentials array lacks the 'primary'
user. This patch adds the 'primary' user to the credentials
array for this test.

[0] http://logs.openstack.org/94/444994/4/check/gate-tempest-dsvm-patrole-admin-ubuntu-xenial-nv/370bc2d/console.html

Change-Id: I62050cc8595acb87b49ecb9e9c6ff80503591bc3
Partial-Bug: #1670553
2 files changed