Runs DS enabled loop in process (#785)

Solves mutex issues, and other issues with the existing teststand
software. And simplifies the unit test structure.

wpilibc/src/main/native/cpp/DriverStation.cpp

@@ -36,6 +36,8 @@ static constexpr double kJoystickUnpluggedMessageInterval = 1.0;
 
 DriverStation::~DriverStation() {
   m_isRunning = false;
+  // Trigger a DS mutex release in case there is no driver station running.
+  HAL_ReleaseDSMutex();
   m_dsThread.join();
 }