Workaround Saucy trying to connect to DBUS

Devstack fails on saucy, because keystone-client calls end up trying to
connect to DBus. This connection fails due to the lack of DISPLAY
variable.

Workaround for bug #1242992

Change-Id: If6daae861128cab311c86beeaaa8fb1418760bf4
Merge commit 'refs/changes/75/84475/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch
Merge commit 'refs/changes/83/86083/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch