Backport FELIX-4663 for DefaultThreadPool Leak

00:05:02,457 | WARN  | p829371392-46513 | eventadmin                       | 78 - org.apache.felix.eventadmin - 1.3.0.redhat-611454 | EventAdmin: Exception: java.lang.OutOfMemoryError: unable to create new native thread
java.lang.OutOfMemoryError: unable to create new native thread
	at java.lang.Thread.start0(Native Method)[:1.7.0_79]
	at java.lang.Thread.start(Thread.java:714)[:1.7.0_79]
	at EDU.oswego.cs.dl.util.concurrent.PooledExecutor.addThread(Unknown Source)
	at EDU.oswego.cs.dl.util.concurrent.PooledExecutor.execute(Unknown Source)
	at org.apache.felix.eventadmin.impl.tasks.DefaultThreadPool.executeTask(DefaultThreadPool.java:101)
	at org.apache.felix.eventadmin.impl.tasks.AsyncDeliverTasks.execute(AsyncDeliverTasks.java:105)
	at org.apache.felix.eventadmin.impl.handler.EventAdminImpl.postEvent(EventAdminImpl.java:106)
	at org.apache.felix.eventadmin.impl.adapter.LogEventAdapter$1.logged(LogEventAdapter.java:281)
	at org.ops4j.pax.logging.service.internal.LogReaderServiceImpl.fire(LogReaderServiceImpl.java:134)[3:org.ops4j.pax.logging.pax-logging-service:1.7.2]
	at org.ops4j.pax.logging.service.internal.LogReaderServiceImpl.fireEvent(LogReaderServiceImpl.java:126)[3:org.ops4j.pax.logging.pax-logging-service:1.7.2]
	at org.ops4j.pax.logging.service.internal.PaxLoggingServiceImpl.handleEvents(PaxLoggingServiceImpl.java:180)[3:org.ops4j.pax.logging.pax-logging-service:1.7.2]
	at org.ops4j.pax.logging.service.internal.PaxLoggerImpl.inform(PaxLoggerImpl.java:145)[3:org.ops4j.pax.logging.pax-logging-service:1.7.2]
	at org.ops4j.pax.logging.internal.TrackingLogger.inform(TrackingLogger.java:86)[3:org.ops4j.pax.logging.pax-logging-service:1.7.2]
	at org.apache.log4j.Category.info(Category.java:614)[3:org.ops4j.pax.logging.pax-logging-service:1.7.2]
	at org.apache.log4j.Logger.info(Logger.java:592)[3:org.ops4j.pax.logging.pax-logging-service:1.7.2]