Later ceph versions allow the crush_rule to be changed on a pool;
add this key with type str to the list of supported keys for
the pool broker.
Change-Id: I2c405f9a4956ff1ccf1edb7372a9bb11e1e591a4
Helper functions for the ceph charms. This library has shared functionality that is used in the ceph-mon, ceph-osd and ceph
charms. Anything that needs to be shared across the ceph charms should live here.