Add test documentation for docs tox target

Enable sphinx to generate documentation from docstrings by running
'tox -e docs'.

Change-Id: I5996e5f07493f69f14172b4bb0535852e89d5456
diff --git a/neutron_tempest_plugin/common/utils.py b/neutron_tempest_plugin/common/utils.py
index ab99db9..c62aa78 100644
--- a/neutron_tempest_plugin/common/utils.py
+++ b/neutron_tempest_plugin/common/utils.py
@@ -73,7 +73,7 @@
     """Wait until callable predicate is evaluated as True
 
     :param predicate: Callable deciding whether waiting should continue.
-    Best practice is to instantiate predicate with functools.partial()
+       Best practice is to instantiate predicate with functools.partial()
     :param timeout: Timeout in seconds how long should function wait.
     :param sleep: Polling interval for results in seconds.
     :param exception: Exception instance to raise on timeout. If None is passed