Perform stop/destroy/remove for remaining services on ServiceController shutdown

SourceForge Submitter: rodburgett .
This patch addresses housekeeping deficiencies in two
classes from the org.jboss.system package.

The ServiceCreator class has no shutdown method but it
does hold a reference to an MBeanServer that is
initialized in it's constructor. The service creator patch
file adds a shutdown() method to null out this reference.

The shutdown method of the ServiceController walks
through it's list of remaining deployed services, calling
the remove() method for each one. This approach
truncates the normal life cycle of services and skips any
cleanup operations that might performed in the stop()
and destroy() methods for the service. This patch adds
calls to stop() and destroy() for each deployed service
in the ServiceController.shutdown() loop.

Also, a new method is added to ServiceController,
cleanupContext(), to perform some cleanup on a
ServiceContext instance. This method is called for each
ServiceContext during the ServiceController.shutdown()
loop.

Finally in the ServiceController, the previously empty
postDeregister() method is updated to call the new
ServiceCreator.shutdown() method and to null out
references to several fields that were initialized by the
preRegister() method.