The new partitioned table capability added a new relkind, namely
RELKIND_PARTITIONED_TABLE. Update fireRIRrules() to apply RLS
policies on RELKIND_PARTITIONED_TABLE as it does RELKIND_RELATION.

In addition, add RLS regression test coverage for partitioned tables.

Issue raised by Fakhroutdinov Evgenievich and patch by Mike Palmiotto.
Regression test editorializing by me.

Discussion: https://postgr.es/m/flat/20170601065959.1486.69906@wrigleys.postgresql.org