Bugfix: Deadlock in queue when lease/reservation runs out

As an example, if Job A locked a resource and Job B reserved a resource but was postponed for a later execution, the reservation was still stored in the ReservedExternalResourceAction even though the lease time run out . This leads to a dead lock for the Job B, because it can't reserve another resource in the ExternalResourceQueueTaskDispatcher ever again.

Change-Id: I45d30c1b85686caff0a5f8a7cce729f7ce1b04de
Remove some object data from serialization

Set the StashInfo fields of the ExternalResource object to transient. This disables the XML serialization per XStream into the main Jenkins configuration.

Change-Id: I815809b96a63c1bd53c9dba5ae7ccb6b59c3d98a
Merge pull request #3 from EBichel/master

Bugfix: Deadlock in queue when lease/reservation runs out