Emulate sync D-Bus method call with async implementation underneath to avoid poll race condition

tests/integrationtests/TestingProxy.h

@@ -61,7 +61,6 @@ protected:
     void onSimpleSignal() override
     {
         m_gotSimpleSignal = true;
-        printf("Thread %d: Got simple signal\n", gettid());
     }
 
     void onSignalWithMap(const std::map<int32_t, std::string>& m) override
@@ -113,6 +112,7 @@ protected:
 
 //private:
 public: // for tests
+    int m_SimpleSignals = 0;
     std::atomic<bool> m_gotSimpleSignal{false};
     std::atomic<bool> m_gotSignalWithMap{false};
     std::map<int32_t, std::string> m_mapFromSignal;