[...]
{%- set host_config_file = grains['nodename'] + ".local.cfg" %}
{% include host_config_file %}
[...]

=>

----------
          ID: /etc/network/interfaces
    Function: file.managed
      Result: False
     Comment: Traceback (most recent call last):
                File "/usr/lib/python2.7/dist-packages/salt/utils/templates.py", line 77, in render_tmpl
                  output = render_str(tmplstr, context, tmplpath)
                File "/usr/lib/python2.7/dist-packages/salt/utils/templates.py", line 169, in render_jinja_tmpl
                  output = jinja_env.from_string(tmplstr).render(**unicode_context)
                File "/usr/lib/python2.7/dist-packages/jinja2/environment.py", line 894, in render
                  return self.environment.handle_exception(exc_info, True)
                File "<template>", line 11, in top-level template code
                File "/usr/lib/python2.7/dist-packages/salt/utils/jinja.py", line 103, in get_source
                  raise TemplateNotFound(template)
              TemplateNotFound: vpn01.local.cfg


but:

root@ops:/srv/salt/fsroot/network/interfaces# ls -1l
total 16
-rw-r--r-- 1 root root  223 Feb  8 01:00 init.sls
-rw-r--r-- 1 root root 2669 Feb  8 00:01 interfaces.H_gw05.paderborn.freifunk.net
lrwxrwxrwx 1 root root   15 Feb  8 01:00 interfaces.H_vpn01.paderborn.freifunk.net -> interfaces.tmpl
-rw-r--r-- 1 root root 1490 Feb  8 01:08 interfaces.tmpl
-rw-r--r-- 1 root root  271 Feb  8 00:08 vpn01.local.cfg