(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.
This test is also testing the behavior of resources and properties when we're just testing the behavior of `update`. This could be done by creating a provider instance, expecting `:install` to be called, and then calling `:update`.