Fixing #5299: variables not used properly.

While installing katello 'community' nighty today I noticed a few errors
related to how certain variables were being refered to in a couple of
templates:

```bash
Variable access via 'fqdn' is deprecated. Use '@fqdn' instead.
template[/usr/share/katello-installer/modules/certs/templates/rhsm-katello-reconfigure.erb]:19
Variable access via 'fqdn' is deprecated. Use '@fqdn' instead.
template[/usr/share/katello-installer/modules/pulp/templates/etc/pulp/server.conf.erb]:40
```

This pull request should fix these variables