Add support for enabling report processor

[cprice404]

This will entail modifying the puppetdb::master::config class in such a way as to support adding the "puppetdb" report processor to the list of report processor. Big "gotchas":

1. Must be backward compatible with previous versions of puppetdb (so basically, it can't add the report processor if the version of puppetdb does not support it, or something similar).
2. Must leave any existing report processors intact (meaning that it will somehow need to parse the existing puppet.conf file before considering modifying the setting).