Fix TestThreadSpecificBreakpoint with LLGS

* Set the state of the process into running/stepping on continue/step operations
* Add mutex to use transactions in Thread State Coordinator
** It is required because the events from two Signal Handler or form a Signal handler and a Resume request shouldn't overlap
* Send Stop Replay Packet only when the state of the process changed

Differential Revision: http://reviews.llvm.org/D7374

llvm-svn: 228387