attempt to fix possible thread-safety problem...

==> mod_wsgi.log <==
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/opt/alerta/lib/python2.6/site-packages/alerta/app/utils.py",
line 141, in wrapped_function
    resp = make_response(f(*args, **kwargs))
  File "/opt/alerta/lib/python2.6/site-packages/alerta/app/views.py",
line 50, in decorated_function
    return func(*args, **kwargs)
  File "/opt/alerta/lib/python2.6/site-packages/alerta/app/views.py",
line 175, in create_alert
    incomingAlert = Alert.parse_alert(request.data)
  File "/opt/alerta/lib/python2.6/site-packages/alerta/common/alert.py",
line 124, in parse_alert
    alert[k] = datetime.datetime.strptime(v, '%Y-%m-%dT%H:%M:%S.%fZ')
AttributeError: _strptime