manifests/repo/apt: Fix the apt::source.

This corrects two really weird things in the way we were managing the
APT repo and the key:

* Stop using a template.
* Switch to using `key_source` and point to the URL of the key.

Of note: WTFBBQ were we doing using a template for a file to begin with?
Chnaged RPM provider to yum or zypper

Using the rpm provider prevents dependancy resolution. As such the user
must ensure that erlang is already present on the system before this
module is applied to the node.
Removed chained erlang dependancy from README

The chaining of the erlang class to esnure erlang is present before this
module is applied no longer required.
Updated test to use yum provider

Previous commits changed the provider to yum rather than rpm in the
puppet manifest. This commit updates the test.
Merge pull request #188 from daenney/fix-apt-key

manifests/repo/apt: Fix the apt::source.
Merge pull request #180 from george-b/remove_rpm_provider

Remove rpm provider