Fix handling of failed exports and service unregistration during export

git-svn-id: https://svn.apache.org/repos/asf/cxf/dosgi/trunk@1514423 13f79535-47bb-0310-9956-ffa450edef68
Refactored/simplified ExportRegistrationImpl, fixed synchronization, replaced ServiceTracker with ServiceListener fixing occasional reference leak when failed export is closed

git-svn-id: https://svn.apache.org/repos/asf/cxf/dosgi/trunk@1514424 13f79535-47bb-0310-9956-ffa450edef68