Fix pep8 failure
Fix pep8 failure

Fix "./os_performance_tools/collectors/mysql.py:54:80: E501 line too long
(87 > 79 characters)"

This is done with reworking the comment to inline the URL.

Change-Id: Ic3b965cdc8d43fdf8621036a0819d2f7df13fb9c

openstack/os-performance-tools