QmlProfiler: managing failed starts gracefully

Change-Id: Ice0debcb6b83977b8f50dd154687e7c5c6abac7b
Reviewed-on: http://codereview.qt.nokia.com/2113
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/plugins/valgrind/valgrindengine.h

@@ -63,7 +63,7 @@ public:
         ProjectExplorer::RunConfiguration *runConfiguration);
     ~ValgrindEngine();
 
-    void start();
+    bool start();
     void stop();
 
     QString executable() const;