Add developement packages support

Add developement packages support

This commits introduces the support of the developpement branches of
Ceph. You can now install Ceph from master.
The behavior is done through 2 new options:

* ceph_stable: true will use the stable branch
* ceph_dev: true will use the dev branch

For the dev packages don't forget to set the branch that you want to
use.

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>