ASACORE-1076 Improve AllJoyn CPU utilization

In my test with multiple single processor virtual machines, AJ Core
often spiked near 100% CPU and things got really slow. An
investigation revealed that the spike was caused by TimerThread
ping-ponging alerts between its controller thread and the respective
IODispatch. This essentially starves new I/Os most notably observed
on machines with single processor.

This fix is to break the cyclic alerts between the two threads by
prioritizing the I/O handle. With this fix, the CPU utilization
improved from over >90% to <5% (during session join). General
performance also improved as well for other scenarios and CPU
configurations (on Windows platform).

Change-Id: I6cb6b0fdb563cdd5f4a015cb77a110669fe94593
Signed-off-by: Way Vadhanasin <wayvad@microsoft.com>