Don't test openstack_groups on stable branches

Without this patch, the stable keystone branches fail the K2K tests
because they don't support the assertion feature added in #1687593 and
we don't intend to backport it. This change allows the stable branches
to still be tested using a regular static group mapping.

Change-Id: Ie1be1cc0e961a1584c99247f0c1b0032576718d8
2 files changed