Add config option to limit image tags

This patch adds the image_tag_quota config option. This allows a deployer
to limit the number of image tags allowed on an image for v2. The default value
is 128. If an image is somehow over the limit, tags can still be removed but no
more may be added.

Fixes bug 1252337
docImpact

Change-Id: I2036e2a88601d7c5aa85fad32d90fe0ed30b84c8
Add config option to limit image members

This patch adds the image_member_quota config option. This allows a deployer
to limit the number of image members allowed per image. The default value
is 128, to be consistent with other quota defaults. Users will only be able
to update an image if the result of the transaction would be under this limit.

This is for both Glance v1 and v2

Fixes bug 1252459
docImpact

Change-Id: I02f5e82ca4c4acf6cd7bc94f9b99086054a616c9
Migrate to oslo.messaging

Glance currently uses a custom notifier and it has been maintaining it
for a long time. In a hope of reducing duplicated code and improving
cross-project contributions, this patch replaces the old notifier with
the one, recently developed, in oslo.messaging.

The oslo.messaging project is a port of the old oslo-rpc code to a
standalone, more stable and improved project. It brings all the benefits
that oslo-rpc would've brought as well as an easier way to integrate
with other projects.

This patch also:

    - Reduces the code shipped along with Glance since all the code
      copied from oslo-incubator related to the notifier is not needed
      anymore.
    - Improves the stability of existing, broker based, notifications.
    - Brings HA support.
    - Keeps backward compatibility by translating the old
      `notifier_strategy` into oslo.messaging drivers.

Changes to the code:

    - It is now necessary to pass the request context to the
      notification call.
    - Notifier package is no longer necessary. A notifier module was
      added instead.
    - New, notifier related, configurations were added.
    - A lot of code was removed

Since there's still not an official release, requirements.txt points to
the latest tarball created. A release for oslo.messaging is planned for
Icehouse.

docImpact
Implements bp oslo-messaging

Change-Id: I8cd84772bc5867e06b2a50ed7e15b9e86f0b94ad
Merge "Migrate to oslo.messaging"