Foreman user provider

This is just a Proof of concept.

This is my first puppet type/provider so feel free to comments and criticize.
My idea is to implement most/all the foreman api with puppet types.

It's working for me but I'm sure there are lot of things to improve.

To create a user you can do:

```puppet
foreman_user { 'foo':
  ensure    => present,
  firstname => 'foo',
  lastname  => 'bar',
  mail      => 'foo.bar@example.com',
  admin     => true,
  password  => 'foobar',
}
```

To delete a user:

```puppet
foreman_user {'foo':
  ensure => absent,
}
```