Some of us may install python-ceph package with other module.
With this new 'manage_packages' parameter, we can avoid an duplicate
package declaration when it's done in an other part of puppet code.
Default behavior is not changed (package will still be installed).
Change-Id: I75ffa9c3dd05ea31f41b032f4778f967b1c6d974
Signed-off-by: Arnaud Morin <arnaud.morin@corp.ovh.com>