qa/suites/upgrade: disable min pg per osd warning
disable the TOO_FEW_PGS warning, as
1ac34a5ea3d1aca299b02e574b295dd4bf6167f4 is not backported to mimic, we
will have TOO_FEW_PGS warnings when a healthy cluster is expected when
upgrading from mimic.
this change disables this warning by setting "mon_pg_warn_min_per_osd" to
"0".
this change is not cherry-picked from master. as
1ac34a5ea3d1aca299b02e574b295dd4bf6167f4 is already included by master,
and we don't perform upgrade from mimic on master branch.
Signed-off-by: Kefu Chai <kchai@redhat.com>