Policy testing checks could be simplified in test_v3_filters

[Henry Nash]

test_v3_filters resets the policy file repeatedly to perform its various checks. Usinf the current code, if you do this within a given test more than once it seems to break, leading to more complex test code. E.g.:

        # TODO(henry-nash) Ideally the policy setting would happen in the
        # entity for-loop below, using a string substitution of 'plural'.
        # However, that appears to lead to unreliable policy checking - i.e.
        # multiple calls to _set_policy doesn't work properly.

        self._set_policy({"identity:list_users": [],
                          "identity:list_groups": [],
                          "identity:list_projects": [])

        for entity in ['user', 'group', 'project']:
              Do some action that needs the policy above for that type of entity

whereas it would be better to reset the policy every time in the loop.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/156597

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/156597
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=9c797ef41cbe13aa826e9e170628725b6c090e40
Submitter: Jenkins
Branch: master

commit 9c797ef41cbe13aa826e9e170628725b6c090e40
Author: Konstantin Maximov <email address hidden>
Date: Tue Feb 17 16:41:24 2015 +0300

    Improved policy setting in the 'v3 filter' tests

    The test case class IdentityTestListLimitCase (test_v3_filters.py)
    always sets multiple policies for the each test defined in that class.
    However, only one policy is really needed for each test case.
    That appears to lead to unreliable policy checking.
    It would be better to set only one policy required for the particular
    test case (policy with the type of entity used in the test case).

    Change-Id: I7892950b43c56ecce03677d8d592e71359bedf27
    Closes-Bug: #1271273