mon: make 'mon {add,remove}_data_pool ...' take pool name or id

Take either a pool name or an id.  Fix up the tests accordingly.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #687 from ceph/wip-pool

mon: make 'mon {add,remove}_data_pool ...' take pool name or id

Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>