This change adds the ability to listen for events across multiple
rabbit queues. Nova cells v2 has a message broker per cell and
the charms already support having a separate message broker for
neutron, in both these topologies ceilometer needs the ability to
listen to multiple brokers.

To achieve this a new relation 'amqp-listener' has been introduced.
The existing 'amqp' relation should be used for the broker that
ceilometer listens to and publishes to. 'amqp-listener' should be
used for additional brokers that ceilometer just listens on.

Update functional tests to satisfy relation with
nova-cloud-controller.

Change-Id: Ifdade3f7814620f4cd4a1d35a584cbc099bb6d88

The ceilometer-upgrade command needs to be run to update back end
ceilometer data stores. When attempting to run this command during
deploy time due to the number of required relations many inherent
race conditions exist leading to Bug#1749280.

This change allows the ceilometer-upgrade command to be run as an action
post-deploy.

Change-Id: I64a56d9a38532476b8a01df6227231a1276c708f
Closes-Bug: #1749280

Update charm to support Ceilometer@Queens; specifically:

 - Removal of Ceilometer API service
 - Removal of ceilometer-collector service

Most of this change is related to dropping of these
services; In addition its now possible to complete a
ceilometer-upgrade without mongodb being configured.

As this charm no longer provides any endpoints to
keystone, for Queens the identity-credentials relation
is required instead of the identity-service relation.

Change-Id: I3cefc24ffc9a0e60f446fbbdff603dfad37f7baa

Implement DNS high availability. Pass the correct information to
hacluster to register a DNS entry with MAAS 2.0 or greater rather
than using a virtual IP.

Charm-helpers sync to bring in DNS HA helpers

Change-Id: I543095a210e668f30c3617990b3ee668a3143dd9

Juju 2.0 provides support for network spaces, allowing
charm authors to support direct binding of relations and
extra-bindings onto underlying network spaces.

Resync charm-helpers to pickup support in API endpoint
resolution code and add API extra-bindings to the charm
metadata.

Change-Id: Ica87935997e116d32beea4cab1a6f12f1de54b54

Update documentation for relations per https://wiki.ubuntu.com/ServerTeam/OpenStackCharms/ReleaseNotes1501#Ceilometer