Runs DS enabled loop in process (#785)

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

wpilibcIntegrationTests/src/FRCUserProgram/cpp/mockds/MockDS.h

@@ -0,0 +1,28 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <atomic>
+#include <thread>
+
+namespace frc {
+class MockDS {
+ public:
+  MockDS() = default;
+  ~MockDS() { stop(); }
+  MockDS(const MockDS& other) = delete;
+  MockDS& operator=(const MockDS& other) = delete;
+
+  void start();
+  void stop();
+
+ private:
+  std::thread m_thread;
+  std::atomic_bool m_active{false};
+};
+}  // namespace frc