Fix min_microversion in volume test_groups_rbac

This PS fixes the min_microversion in volume test_groups_rbac
which is incorrectly 3.14 when in fact it should be 3.13 [0] according
to Cinder microversion documentation. This change will also make Patrole
consistent with Tempest [1].

[0] https://docs.openstack.org/cinder/latest/contributor/api_microversion_history.html#id13
[1] https://github.com/openstack/tempest/blob/c536175d8d4d572278b4e592dadc548b34e4ea91/tempest/api/volume/admin/test_groups.py#L27

Change-Id: I9b19d44e25057d688e4b968cab2a047049658344
1 file changed