CTest: Improve stop-time implementation

The CTestTestStopTime test has been failing sporadically because the
stop time causes the first internal test to have a timeout short enough
that we might hit it and start the second test just before the stop time
is reached.  Instead we should track when a timeout is shortened in
order to stay within the stop time.  If a test times out for this reason
then we should consider the stop time reached and not start any more
tests.

Source/CTest/cmCTestMultiProcessHandler.h

@@ -113,6 +113,9 @@ protected:
   inline size_t GetProcessorsUsed(int index);
   std::string GetName(int index);
 
+  bool CheckStopTimePassed();
+  void SetStopTimePassed();
+
   void LockResources(int index);
   void UnlockResources(int index);
   // map from test number to set of depend tests
@@ -125,7 +128,7 @@ protected:
   size_t RunningCount;
   std::set<size_t> ProcessorsAvailable;
   size_t HaveAffinity;
-  bool StopTimePassed;
+  bool StopTimePassed = false;
   // list of test properties (indices concurrent to the test map)
   PropertiesMap Properties;
   std::map<int, bool> TestRunningMap;