Fixing issues in policy regression failures in R2.0 - Build 8.

1. In PolicyFixture made changes to _delete_policy(), so that
policy is deleted only if present in quantum records.
   This Fixes:
        test_create_api_policy
        test_associate_disassociate_api_policy

2. Moved _create_n_policy_n_rules() from policy_test_utils to
policy_test_helpers, because there was a problem of cyclic import.
Moreover this routine makes more sense as a helper function while
creating multiple rule policies.
   This Fixes:
        test_policy_rules_scaling_with_ping

3. Fixed vnc_api import issues in policy_test_utils.
   This Fixes:
        test_policy_rules_scaling_with_ping
        test_policy_rules_scaling_with_ping_api

4. 'result' was not initialized before use in test_policy.py
   This Fixes:
        test_policy_with_multi_vn_in_vm

Change-Id: I3c600a3cc02f47411e6929abc688899e9b9326ca