Make HDScanner a Daemon Thread

Marking the daemon flag to true will allow the VM to exit upon server shutdown. Alternatively, kill the scanner upon undeploy.

"HDScanner" prio=1 tid=0x00007f722c171100 nid=0x356 waiting on condition [0x00007f723c560000..0x00007f723c560d70]
at sun.misc.Unsafe.park(Native Method)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:118)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1841)
at java.util.concurrent.DelayQueue.take(DelayQueue.java:131)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:533)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:526)
at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:470)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:674)
at java.lang.Thread.run(Thread.java:595)