Keystone - List user groups 'membership_expires_at' attribute
Keystone - List user groups 'membership_expires_at' attribute

With the introduction of expiring group memberships, there is a
new attribute `membership_expires_at` when listing user groups.
This patch updates the test to check the attribute and then
ignore it for group dict comparison.

Change-Id: I4294a879071dde07e5eb1da4df133de8032e1059
Partial-Bug: 1809116

cisco-openstack/tempest,cisco-openstack/tempest,openstack/tempest,openstack/tempest