rbd: add wrapper for rbd_pool_metadata_set()
rbd: add wrapper for rbd_pool_metadata_set()

Add wrapper for rbd_pool_metadata_set() function which sets pool metadata
associated with the given key.

Signed-off-by: Mudit Agarwal <e5356c34e3b3b8ef2f9750bb431df6fcd5e2fa6e@redhat.com>

ceph/go-ceph,ceph/go-ceph,ceph/go-ceph