Description of problem:
foreman-proxy generating wrong URLs using foreman_url() for pxe* templates.
They are pointing to Foreman, not smart proxy.

1. Add smart proxy with enabled templates plugin;
2. Create test provision template containing following lines:
   

   foreman_url: <%= foreman_url %>
   foreman_url('provision'): <%= foreman_url('provision') %>
   

3. Create test PXELinux template containing following lines:
   

   foreman_url: <%= foreman_url %>
   foreman_url('provision'): <%= foreman_url('provision') %>
   

4. Create test host, assign test templates and put it to build mode;
5. Execute following commands:
   

   # curl 'http://smartproxy:8000/unattended/provision?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611' | grep foreman_url
   # curl 'http://smartproxy:8000/unattended/PXELinux?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611' | grep foreman_url
   

Actual results:

# curl 'http://smartproxy:8000/unattended/provision?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611' | grep foreman_url
foreman_url: http://smartproxy:8000/unattended/built?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611
foreman_url('provision'): http://smartproxy:8000/unattended/provision?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611

# curl 'http://smartproxy:8000/unattended/PXELinux?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611' | grep foreman_url
foreman_url: http://foremanbox:80/unattended/built?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611
foreman_url('provision'): http://foremanbox:80/unattended/provision?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611

Expected results:

# curl 'http://smartproxy:8000/unattended/provision?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611' | grep foreman_url
foreman_url: http://smartproxy:8000/unattended/built?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611
foreman_url('provision'): http://smartproxy:8000/unattended/provision?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611

# curl 'http://smartproxy:8000/unattended/PXELinux?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611' | grep foreman_url
foreman_url: http://smartproxy:8000/unattended/built?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611
foreman_url('provision'): http://smartproxy:8000/unattended/provision?token=cd1cb7ba-d642-4cc0-a5dd-f30e15490611