Added docs and made template filename variable

Changed how jinja ENV is created
Added docstrings to functions in template.py
Renamed _location_types private attribute of
 SingleInstanceConfigTemplate to _config_paths
SingleInstanceConfigTemplate constructor now uses filename based on
 service type
SingleInstanceConfigTemplate render method now returns the result
Tests updated to use new style of render method
mysql.config.template duplicated to percona.config.template

implements blueprint redis-servicetype

Change-Id: Id9317b560236d5d4967b888d0dc3a4135f1822dc