Use OpenStack Incubated branding for docs

Barbican is not integrated but incubated. The branding of the web pages at
http://docs.openstack.org/developer/barbican/ should thus be the incubated
branding.

Change-Id: I78a0c988993d9d2947769ee412cb962cb6c4ccde
Merge "Use OpenStack Incubated branding for docs"