test: reduce the chance to have degraded PGs

test: reduce the chance to have degraded PGs

in test_mon_osd_misc(), there is good chance that the cluster chooses
to use an unbalanced weight because of the data distribution at that moment.
but this setting could prevent the CRUSH from choosing enough number of
OSDs for test_mon_cephdf_commands(), where 32 PGs are to be created. so
it's more likely that the CRUSH fails to pick enough OSDs for all PGs.
that's why we have a curr_object_copies_rate = 0.5.

so, in this change, pg=pgp=1 is specified for the new pool.

Fixes: http://tracker.ceph.com/issues/22711
Signed-off-by: Kefu Chai <kchai@redhat.com>