TEIIDDES-1931: Stop stackoverflow exceptions from the TeiidServerManager

* ModelerCore
 * As soon as a new instance of TeiidServerManager is constructed assign
   it to the singleton so that no other instances are attempted to be
   constructed. This can happen if restoreState calls listeners which in
   turn require the server manager through ModelerCore. The sync mutex
   object will not prevent this use-case since it would occur in the same
   thread.

* TeiidServerManager
 * While restoring stop any notification of listeners from the initialising
   Teiid instances. Since the manager is in the middle of restoring
   unexpected behaviour can occur from the listeners including stack
   overflow exceptions.