Add finer granularity to host aggregate APIs

This change provides the ability to set finer permission rules around
the host aggregate APIs. Prior to this change, all operations assumed
that the same permissions were necessary. However, it's very possible
that an OpenStack administrator may want to have varying sets of
permissions for operations across the standard CRUD operations.  This
change is only applicable to the v3 APIs as v2 APIs should remain
backwards compatible.

Also included is a change to fake_policy.py (since the file was
updated anyway) to make the base aggregate policy require the
'admin_api' rule (i.e., to be consistent with the policy.json file).

Also added the corresponding API test cases.

DocImpact v3 host aggregate APIs require action-level policies
Implements: blueprint aggregate-api-policy

Change-Id: I8a88824bbb41807fad849ad15af4411d3a3dca6e
Merge "Add finer granularity to host aggregate APIs"