Unable to use run stages with OpenStack

While trying to run PKB with --run_uri, pickle is stuck in never ending loop and fails with:

```
maximum recursion depth exceeded while calling a Python object
```

After some digging, I've found out that the issue is with **getattribute** method stuck in never ending loop in perfkitbenchmarker/providers/openstack/utils.py:

```
File "perfkitbenchmarker/providers/openstack/utils.py", line 80, in __getattribute__
return self.__client.__getattribute__(item)
```