WFLY-3892

DomainLifecycleUtil.start() does not work if DomainLifecycleUtil.stop() is used to stop the host.

Addition of parameter closeConnectionBeforeStop that the user can reset during the tests in order not to close the Connection when stopping the host.
This should be in closeConnection(). If the connection is closed, the domainClient is no longer usable and the ref needs to be nulled.