Debugger: Do not run engines twice

There seems to be race in the LLDB setup on Linux. Work around
by not doing serious work twice to be able to use the test at least.

Change-Id: I387a57d3c66e6c4209bd424af9be16f17acb98fa
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

share/qtcreator/debugger/lldbbridge.py

@@ -94,6 +94,7 @@ class Dumper(DumperBase):
         self.process = None
         self.target = None
         self.eventState = lldb.eStateInvalid
+        self.runEngineAttempted = False
 
         self.executable_ = None
         self.startMode_ = None
@@ -612,6 +613,9 @@ class Dumper(DumperBase):
             % (state, error, self.executable_), args)
 
     def runEngine(self, args):
+        if self.runEngineAttempted:
+            return
+        self.runEngineAttempted = True
         self.prepare(args)
         s = threading.Thread(target=self.loop, args=[])
         s.start()