Docstrings should not start with a space

As per OpenStack Docstrings guide lines [1]:
[H401] Docstrings should not start with a space.

[1] http://docs.openstack.org/developer/hacking/#docstrings

trivialfix

Change-Id: Ifdff563f3ab7559e68c7201575045013db7383a5

watcher/decision_engine/cluster/history/base.py

@@ -59,7 +59,7 @@ in any appropriate storage system (InfluxDB, OpenTSDB, MongoDB,...).
 import abc
 import six
 
-""" Work in progress Helper to query metrics """
+"""Work in progress Helper to query metrics"""
 
 
 @six.add_metaclass(abc.ABCMeta)