tests: cephtool/test.sh wait_for_clean after PG (re)mapping

tests: cephtool/test.sh wait_for_clean after PG (re)mapping

A get/set command may fail with

   Error EBUSY: currently creating pgs, wait

if issued before the PGs are clean. Call wait_for_clean after the pool
is created or a pool setting is changed and remaps the PGs it
contains (size, pg_num...) to ensure the PGs are clean and the set/get
command that follow will succeed.

http://tracker.ceph.com/issues/11624 Fixes: #11624

Signed-off-by: Loic Dachary <ldachary@redhat.com>