Compile Horizon message catalogs during stack.sh

Recently compiled message catalogs (mo files) were removed
in Horizon and django_openstack_auth repositories.
We need to compile message catalogs to make translations
available for Horizon users. It is useful for developers too.

Change-Id: I0831e8308205c116d8e3bb8b43be7f0dd6fa0c0a
Merge commit 'refs/changes/03/127603/4' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch
Merge commit 'refs/changes/11/129211/1' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch