glusterfs driver CI failing on maintenance branches due to incompatible tempest version

[Csaba Henk]

This bug is essentially https://bugs.launchpad.net/devstack-plugin-glusterfs/+bug/1519012 refacing, just in a different way, due to the partiality of the fix for said bug.

The fix, https://review.openstack.org/248789, adjusted the tempest commit so that it works on master, but that then rendered tempest broken for the other branches.

We need a branch-aware conditional tempest checkout.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/255712
Committed: https://git.openstack.org/cgit/openstack/devstack-plugin-glusterfs/commit/?id=92c20721210cb0c3649ad9a21cd7c76f9cc92b12
Submitter: Jenkins
Branch: master

commit 92c20721210cb0c3649ad9a21cd7c76f9cc92b12
Author: Ramana Raja <email address hidden>
Date: Mon Nov 23 21:30:24 2015 +0530

    manila: branch aware Tempest checkout

    Another take on the problem described
    in 5b4dd3c, ie. Manila Tempest update
    in

    https://github.com/openstack/manila/commit/6b8319e32a94c228ff4258cf31dcd6c271350e1c?diff=unified#diff-e0705abec56bf0f83781d686e109d63eR63

    Instead of checking out $MANILA_TEMPEST_COMMIT
    blindly (ie. even if it's unset), we add a
    fallback to the Tempest commit used prior to
    5b4dd3c.

    Change-Id: Idec3924a1b5476683e5520f83df8561d0bd0ccfd
    Closes-Bug: #1524642