QPID-4516: Sporadic failure in ha_tests test_failover_send_receive

Several fixes were required in the code to correct this problem:

- Missing break statement in switch.
- Remove unused function HaBroker::resetMembership
- Abort connection of timed-out backups so they can attempt to reconnect.
- New primary resets membership before allowing backups to connect.
- Test for and ignore double-promotion.
- HaBroker: dynamic logPrefix() shows status. Made status atomic for efficient access for log messages.
- Update primary status in membership.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1432273 13f79535-47bb-0310-9956-ffa450edef68