Added new ext pillar Pepa

New Ext. Pillar Pepa. Configuration templating using Hierarchical substitution and Jinja.

More info can be found at: https://github.com/mickep76/pepa

This was initially written for the ticket #6818.
Standard library modules won't need this `try/except`, only 3rd party modules or, modules which exist in Py2.7 and not in Py2.6(for example)