QPID-5715: [Java Broker] Make virtualhostnode respect states ACTIVE and STOPPED

* Added test to ensure that the VHN can transit between ACTIVE <=> STOPPED
* Fixed defect whereby the VHN could not be recovered in the STOPPED state.  Added test case.
* Fixed defct whereby on stopping a VHN, the DurableConfigurationStore would be left open.

Work by me and Andrew MacBean <andymacbean@gmail.com>.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1594903 13f79535-47bb-0310-9956-ffa450edef68