Add gettext install.
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 <8a35dafb21031d5c8209b1c0c47aaf0390b56a0e@cloudscaling.com>
Approved: Monty Taylor <37c07a49ee3d5191376d758eb1d8298b34456b8e@inaugust.com>
Tested-by: Jenkins

zancas/hacking,openstack-dev/hacking,zancas/hacking,hyakuhei/cleantox,hyakuhei/cleantox,openstack-dev/hacking