QPID-4745: HA safe port allocation for brokers in HA tests.

Many HA tests use --port=0 to start a broker on an available port, but then need
to shutdown and restart the broker on the same port. This is not safe, on a busy
system it is possible for another process to take the port between the time the
broker is shut down and the time it is restarted.

The solution is to do bind(0) and listen in the python test framework (class
HaPort) and let the broker use the socket using qpidd --socket-fd. When the
broker is shut down the port remains bound by the python process. When the
broker is re-started it again is given access to the socket via --socket-fd.

Other changes
- move ha_store_tests into ha_tests.
- add heartbeats to avoid stalling.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1482881 13f79535-47bb-0310-9956-ffa450edef68