mon: add the osd crush rename-bucket command

mon: add the osd crush rename-bucket command

The synopsis is:

 osd crush rename-bucket name1 name2

It is made idempotent by interpreting -EALREADY as returned by
CrushWrapper::rename_bucket return as success.

The crush_rename_bucket method first checks for errors with
CrushWrapper::can_rename_bucket if there is no pending crush so that it
can return early and avoid the creation of a pending crush map.

If renaming is possible, CrushWrapper::rename_bucket is called on the
pending crush map (and creates it indirectly if it does not already
exists).

http://tracker.ceph.com/issues/9526 Fixes: #9526

Signed-off-by: Loic Dachary <loic-201408@dachary.org>