Add gettext install.

When we pulled this from nova, the gettext.install went away, but it
turns out that it's super important, otherwise the import test gets
messed up by _ and our assumption that it gets imported from the
execution entrypoints in bin/ and the test runner.

Change-Id: I7e51d93c44af9f08d7177097c3992127d5851ce0
Reviewed-on: https://review.openstack.org/26970
Reviewed-by: Joe Gordon <jogo@cloudscaling.com>
Approved: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins