Adds a flag to determine whether to reload the rules in policy

Initing a Enforcer class with rules can not set rules,  because the policy
file is modified , the load_rules always try to load the rules from the cache
or config file when checks the policy. This patch adds a flag to determine
whether to reload the rules from policy file.

Closes-Bug: #1279198

Change-Id: Ife84189be4b86a3ee90da4539ff2dbed125be23d
Use mock.call_count to assert the call counter

In patch https://review.openstack.org/#/c/65424 , the unit test for
test_base_filter.py is not using mock.call_count to identify the
call counter.

This patch was using call_count to check that the filter was only
called once.

Change-Id: I792c894c0414d11ab7461b6e5cc9366ced787ebb
Merge "Use mock.call_count to assert the call counter"
Merge "Adds a flag to determine whether to reload the rules in policy"