mon: warn if pg to osd ratio is too low

If there are not enough PGs relative to the number of in osds, warn.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/PGMonitor: health warn if pg_num != pgp_num

Users need to adjust pg_num *and* pgp_num for split but may forget to do
both.

Signed-off-by: Sage Weil <sage@inktank.com>
mon/PGMonitor: health warn if pool has relatively high objects/pg

If there is a pool that has a high objects/pg relative to the rest of the
cluster, warn, as this suggests this particular pool may have too few
PGs.

Signed-off-by: Sage Weil <sage@inktank.com>
vstart: set 'mon pg min per osd'

We need to tweak this since we create relatively few pgs per osd.

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