(PUP-3618) Include pkgng provider for FreeBSD

To improve the default state of Puppet on FreeBSD systems, !his work
moves the pkgng provider into core.  Previously, users of the provider
would need to install from the forge module zleslie/pkgng.
Since this is picking values out of `@property_hash` this doesn't actually query the system. The RPM package provider [intentionally queries the system](https://github.com/puppetlabs/puppet/blob/master/lib/puppet/provider/package/rpm.rb#L76) and calls out [Redmine 1243](http://projects.puppetlabs.com/issues/1243) as the reason why. Is it safe to use a cached value here?