Add function drop_unique_constraint()

We forgot to copy this function from nova, so we are not able to
switch to oslo sqlalchemy.utils until add this function.

Sqlalchemy doesn't supports some sqlite column types so we have no
possibility to drop unique constraint in general way on sqlite (we
loose these column types after migration).
Added unified drop_unique_constraint() function to drop unique
constraint for sql backends with tests.

blueprint: oslo-sqlalchemy-utils

Change-Id: I34000ad2277a97c31a29539d047faaf19876c9d5
Fix hostname conflict in config generator

When the system hostname is the same as a default value in the
config, the _sanitize_default function may replace it incorrectly.
This change checks that the name of the option contains the
substring 'host' to make sure it isn't changing non-hostname
defaults.

Fixes bug 1205411

Change-Id: I93edb2902304c5cd9bfa817b1bccdaec5d807e6c
Refactors boolean returns

Return the boolean evaluation itself rather than
a boolean after evaluation

Change-Id: I6329d474c921e29eb3a690270de12d51cb863710
Fix policy default_rule issue

This patch fixed the following issue in policy:

    1. Default_rule wasn't set correctly when using enforcer.
    2. When overwrite=True set_rule method doesn't work.
    3. Add type check in __missing__ of dict and return
       the correct value of default_rule.
    4. Partially refactor the test_policy code based on the
       related change.

Fixed #bug 1202771

Change-Id: I9be1ac8bdc995adae201e9b45ee124dd525e4822
Import common quota code from nova and cinder

Quota code was imported and merged from nova and cinder projects.

blueprint common-quota

Change-Id: Idc9a85fddd1665ae010bcc4740963e14d81310c3
Update references with new Mailing List location

Yesterday, openstack@lists.launchpad.org was migrated with
all users to openstack@list.openstack.org.

This patch updates references to the old mailing list with the
new, to ensure that people encountering them don't accidentally
try and join the old list!

Change-Id: I170b02bde2d3b93ddefb27452135dc09b23236de
Merge "Fix hostname conflict in config generator"
Merge "Refactors boolean returns"
Merge "Add function drop_unique_constraint()"
Merge "Import common quota code from nova and cinder"
Merge "Update references with new Mailing List location"
Merge "Fix policy default_rule issue"