Added pulp::admin to install and configure pulp-admin tool

Makes it easier to add pulp-admin to the server or another admin machine.
You'll need to add an admin.conf template in the template directory. 

See https://github.com/pulp/pulp_packaging/blob/master/puppet/pulp/templates/consumer.conf.erb for an example and https://docs.puppetlabs.com/guides/templating.html for docs if you're not familiar with templates. 

I'm not an expert on Puppet (let alone Ruby) so if there's a neater way to do it than what's in consumer.conf.erb, I'd love to see it!