Syncing policy engine from oslo-incubator

Syncing policy module - commit a53c4dc
Includes patch 0da5de6 implementing Blueprint policy-constant-check

python update.py --nodeps --base keystone --dest-dir ../keystone/ --modules policy

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Adds the ability to check any resource's field against a constant
(literal, or string) in the policy.json file.

For instance, I can ensure that only users with field `enabled` set to
False can be deleted with the following rule:
"identity:delete_user": "False:%(target.user.enabled)s",

Or that only the `Member` role can be granted:
"identity:create_grant": "'Member':%(target.role.name)s",
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Change-Id: I054271306f20aac47ce5e9dac594bc1989fee56d
Implements: blueprint policy-constant-check
Remove copyright from empty files

According to policy change in HACKING:
http://docs.openstack.org/developer/hacking/#openstack-licensing
empty files should no longer contain copyright notices.

Change-Id: I65e85baf72cf1a413c4b4c8c478587246d4c319a
Closes-Bug: #1262424
Merge "Remove copyright from empty files"
Merge "Syncing policy engine from oslo-incubator"