Adding qpid support to cinder

Moving all qpid parameters under default["openstack"]["block-storage"]
["mq"]["qpid"] so that other qpid options can be added under it. Rabbit
parameters will be brought under "mq" eventually. MQ is selected
through default["openstack"]["block-storage"]["mq"]["service_type"].
Default is "rabbitmq".

Implements: blueprint qpid-activemq-support
Change-Id: I4c45a1aa8f6a6a505c8a1494d02f8bf5bc19dbfe
Relax the dependency on openstack-identity to the 7.x series

openstack-identity is now on 7.2.0, which doesn't get picked up because of the
strict dependency of the 7.0.x series. CHANGELOG cleanup.

Change-Id: I319c6d458e8c36dfb2545319b5f9b35383f8ff5e