osd/OSDMap: get_up_osd_features()

Signed-off-by: Sage Weil <sage@inktank.com>
mds: require CEPH_FEATURE_OSD_TMAP2OMAP

Require that all OSDs support TMAP2OMAP before starting the MDS.  This
avoids doing some work and then crashing with EOPNOTSUPP, and gives us
a more informative message in the logs.

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