QPID-4390: Change VHC to store the default HOUSEKEEPING_CHECK_PERIOD. Clear the current actor in tear down if test sets the current actor

git-svn-id: https://svn.apache.org/repos/asf/qpid/branches/java-broker-config-qpid-4390@1433439 13f79535-47bb-0310-9956-ffa450edef68