Sync policy from oslo-incubator

Sync latest policy module at ddd63a7346bb57a47b0cd031608fc9475d68e241 to
help remove it's dependency for jsonutils. It also fixes some
bugs and introduces new option "policy_dirs", allow developer to add
some policy files in multiple directories.

Change-Id: Ibdb5832712d843ccce29c945cfbe4570dc5799aa
Merge "Sync policy from oslo-incubator"