Bug 930 - Add bound to queue in SingletonHandler#NOTIFICATION_EXECUTOR .

Add queue capacity with hardcoded value 10. When maxPoolSize + queue capacity
is reached, caller thread will be blocked.
Mark thread as interrupted when catching InterruptedException, propagate it
to caller.
Remove code that pushed first two runnables to queue when core size was
reached - saturate whole threadpool capacity first.

Change-Id: I9c52b52eac127bea0cbb2abf7a65c0165daf8895
Signed-off-by: Tomas Olvecky <tolvecky@cisco.com>