mon: OSDMonitor: split 'osd pool set' out of 'prepare_command'

We should start doing this across the whole 'prepare_command' function.
Makes it prettier to the reader, and easier to add new code.

Change the command to send a string instead of an int to allow us to have
non-integer pool paramters that can be modified.  Support input json with
both int and string values so that we work with all flavors of client.

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: OSDMonitor: allow (un)setting 'hashpspool' flag via 'osd pool set'

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
osd: osd_types: Output pool's flag names during dump

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
osd/osd_types: generalize pg_pool_t::get_flags_string()

This way the method doesn't have to be modified when new flags are added.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #712 from ceph/wip-mon-pool-set

rework ceph osd pool set <pool> <field> <val>

Reviewed-by: Sage Weil <sage@inktank.com>