mon: fix inverted test in osd pool create

When using the properties key=value only, the test was inverted
and an attempt to obtain a substring at index string::npos throws
an exception.

Add variations of osd pool create to qa/workunits/mon/pool_ops.sh
to assert the problem has been fixed and all code paths are used.

http://tracker.ceph.com/issues/6357 fixes #6357

Signed-off-by: Loic Dachary <loic@dachary.org>