Ability to enable/disable management of the vcl includes if given custom vcl template.

I just started using this module and I need to have custom vcl directives (so a custom template) and I ran across this issue:

Could not find dependent Exec[concat_/etc/varnish/includes/waf.vcl] for File[/var/lib/puppet/concat/_etc_varnish_includes_waf.vcl/fragments/02_waf] at /etc/puppet/modules/concat/manifests/fragment.pp:120

I think this was because the concat for the waf include was not getting initialized if a custom template was specified.  I added a parameter to manage the includes if a custom vcl was used which seems to work.

This patch should leave all existing functionality with the normal vcl template untouched but it can allow for a totally custom vcl file with no management of includes or a working partial vcl override that still uses the puppet defined includes.

Thanks,
Adrian