Add ability to purge config

This patch adds paramters to the api and registry
classes that allows the respective config files to
be purged.

This is needed when running in a configuration that
is contrary to the defaults for the platform packager,
such as rabbitmq on RDO

Change-Id: I9f8664b2098bd41b9a98eac095bfec8493ed1254
Merge "Add ability to purge config"
Merge git://github.com/puppetlabs/puppetlabs-glance