This patch implements upgrading keystone with zero downtime as the
default installation process. Handlers have been modified to ensure that
the first keystone node is stopped, facilitates the database migrations,
and that it is started and available before restarting any other keystone
nodes. Migrations also now only occur when there is a change within the
installed keystone venv.
This process is documented at
http://docs.openstack.org/developer/keystone/upgrading.html#upgrading-without-downtime
A new test scenario has been added for testing basic upgradability
between releases.
Implements: blueprint upgrade-testing
Change-Id: I0d3cfcb80b64d005d60f4c8445f991855f844796
04737f5dbd