only launch core nodes if master was launched by roslaunch

tools/roslaunch/src/roslaunch/launch.py

@@ -382,6 +382,9 @@ def _launch_nodes(self):
     def _launch_master(self):
         """
         Launches master if requested. 
+        @return: True if a master was launched, False if a master was
+        already running.
+        @rtype: bool
         @raise RLException: if master launch fails
         """
         m = self.config.master
@@ -426,6 +429,8 @@ def _launch_master(self):
             self.logger.info("setting /roslaunch/uris/%s__%s' to %s"%(hostname, port, self.server_uri))
             param_server.setParam(_ID, '/roslaunch/uris/%s__%s'%(hostname, port),self.server_uri)
 
+        return not is_running
+
     def _check_and_set_run_id(self, param_server, run_id):
         """
         Initialize self.run_id to existing value or setup parameter
@@ -627,8 +632,9 @@ def _setup(self):
             self.remote_runner.add_process_listener(self.listeners)            
 
         # start up the core: master + core nodes defined in core.xml
-        self._launch_master()
-        self._launch_core_nodes()        
+        launched = self._launch_master()
+        if launched:
+            self._launch_core_nodes()
 
         # run exectuables marked as setup period. this will block
         # until these executables exit. setup executable have to run