roles/koji-builder: Deploy the Koji builder

The *koji-builder* role installs and configures the Koji builder
(*kojid*). It supports configuring an HTTP proxy, if required.

roles/koji-builder/templates/http_proxy.conf.j2

@@ -0,0 +1,10 @@
+[Service]
+{% if http_proxy|d %}
+Environment=http_proxy={{ http_proxy }}
+{% endif %}
+{% if https_proxy|d %}
+Environment=https_proxy={{ https_proxy }}
+{% endif %}
+{% if no_proxy|d %}
+Environment=no_proxy={{ no_proxy|join(',') }}
+{% endif %}