Log traceback output when batch action subprocess fails

tailbone/views/batch/core.py

@@ -962,7 +962,13 @@ class BatchMasterView(MasterView):
 
         # run command in subprocess
         log.debug("launching command in subprocess: %s", cmd)
-        subprocess.check_call(cmd)
+        try:
+            subprocess.check_output(cmd, stderr=subprocess.PIPE)
+        except subprocess.CalledProcessError as error:
+            log.warning("command failed with exit code %s!  output was:",
+                        error.returncode)
+            log.warning(error.stderr.decode('utf_8'))
+            raise
 
     def action_subprocess_thread(self, key, port, username, handler_action, progress, **kwargs):
         """