gettextutils: fix translation domain

Fixes bug #1076285

When oslo-incubator code gets copied into a project, the project's
l10n infrastructure will extract translatable messages from the
oslo code into the project's message catalog. Translations of those
messages will not be found if we use 'openstack.common' as the
translation domain.

Instead, use 'oslo' as the translation domain and update.py will
change this to the project name.

Change-Id: I7ab46c4f860c9c307758ab63002ae410e4f975fe
Merge "gettextutils: fix translation domain"