Fix memory leak because of persistent browser history.

Clear the Browser history (storing (request, response)) after each
suite. Moreover, it does make sense to keep it as suites are independent of
each other.

erp5/util/benchmark/process.py

@@ -124,6 +124,12 @@ class BenchmarkProcess(multiprocessing.Process):
             raise RuntimeError("Stopping as mean is greater than maximum "
                                "global average")
 
+      finally:
+        # Clear the Browser history (which keeps (request, response))
+        # otherwise it will consume a lot of memory after some time. Also it
+        # does make sense to keep it as suites are independent of each other
+        self._browser.mech_browser.clear_history()
+
       result.exitSuite(with_error)
 
     result.iterationFinished()