Rename Savanna to Sahara

It was decided to rename Savanna project to Sahara to avoid potential
trademark issues. Repos renaming planed for March 12.

http://lists.openstack.org/pipermail/openstack-infra/2014-March/001003.html

Change-Id: I8fdc20ed2b55490412e9a05f6a6aa12bf833e6e5