Reset policies after RESOURCE_ATTRIBUTE_MAP is populated

Reset policies after RESOURCE_ATTRIBUTE_MAP is populated

The REST API relies on neutron-specific policy checking logic that is
only available after the extensions are loaded and the
RESOURCE_ATTRIBUTE_MAP is populated. This patch resets the policies
immediately after these steps are done. This ensures that in the event
the policies are prematurely loaded for any reason, the on-demand
loading of the policies will reload the policies and properly configure
the neutron specific checks on the next policy check.

Change-Id: Ic2ab3f0179b0c192e63af0bc4268d92aa26bdabe
Closes-Bug: #1398566
Related-Bug: #1254555