mon/OSDMonitor: accept crush_device_class in 'osd new' json input

mon/OSDMonitor: accept crush_device_class in 'osd new' json input

If provided, set the OSD device_class at OSD creation time.  This is
simpler than writing a file that the OSD has to read in and use to
set its initial device class, and also avoids a bit of sticky state
at the OSD that will make it keep trying to reset its device class on
startup if it ever gets cleared.

Note that we now ignore json input fields we don't understand, so remove
a test case.

Signed-off-by: Sage Weil <sage@redhat.com>