bugfix: DNS domain forward server syntax

When generating a configuration for DNS domain forward to a local server
with 'set service dns forwarding domain foo.com server 1.1.1.1' this resulted in

  # domain ... server ...
  forward-zones=bar.com = 2.1.1.1;2.1.1.2
  forward-zones=foo.com = 1.1.1.1;1.1.1.2

On PowerDNS recursor restart the last line won and it totally forgot about
'bar.com'. This could be seen from the logfiles that only one domain was loaded:

  Redirecting queries for zone 'foo.com.' to: 1.1.1.1:53, 1.1.1.2:53

The manual at https://doc.powerdns.com/3/recursor/settings/#forward-zones shows
that all domains have to be configured on one 'forward-zones=' line. In the above
example this has to result in:

  forward-zones=bar.com=2.1.1.1;2.1.1.2, foo.com=1.1.1.1;1.1.1.2

A subsequent check within the logfiles reveal that it's now working:

  Redirecting queries for zone 'bar.com.' to: 2.2.2.2:53, 2.2.2.1:53
  Redirecting queries for zone 'foo.com.' to: 1.1.1.1:53, 1.1.1.2:53

1 files changed, 5 insertions, 4 deletions

diff --git a/src/conf-mode/vyos-config-dns-forwarding.py b/src/conf-mode/vyos-config-dns-forwarding.py
index 5494d07aa..be48cde60 100755
--- a/src/conf-mode/vyos-config-dns-forwarding.py
+++ b/src/conf-mode/vyos-config-dns-forwarding.py
@@ -51,9 +51,10 @@ local-address={{ listen_on | join(',') }}
 # domain ... server ...
 {% if domains -%}
 
-{% for d in domains -%}
-forward-zones={{ d.name }}={{ d.servers | join(";") }}
-{% endfor -%}
+forward-zones={% for d in domains %}
+{{ d.name }}={{ d.servers | join(";") }}
+{%- if loop.first %}, {% endif %}
+{% endfor %}
 
 {% endif %}
 
@@ -184,7 +185,7 @@ def generate(dns):
     if dns is None:
         return None
 
-    tmpl = jinja2.Template(config_tmpl)
+    tmpl = jinja2.Template(config_tmpl, trim_blocks=True)
 
     config_text = tmpl.render(dns)
     with open(config_file, 'w') as f: