Add support for specifying the default vhost.

Nginx lacks a strict-sni option like haproxy, so allow specifying
the default container to receive random traffic not matched by
other hosts.

Dockerfile

 FROM csmith/service-reporter-lib:latest 
-MAINTAINER Chris Smith <chris87@gmail.com> 
+MAINTAINER Chris Smith <dke@chameth.com> 
 
 RUN \
   pip install \

README.md

 
 * `com.chameth.proxy=<port>` -- specifies the port on the container that the
   proxy should connect to
+* `com.chameth.proxy.default` -- identifies the container that will receive
+  traffic if no others match
 * `com.chameth.proxy.protocol=<protocol>` -- the protocol to use when
   connecting to the container. Optional, defaults to HTTP.
 * `com.chameth.vhost=<host>` -- the virtual host that the proxy will accept

generate.py

   services = []
   domains = {k: v.split(',') for k, v in fetcher.get_label('com.chameth.vhost').items()}
   protocols = fetcher.get_label('com.chameth.proxy.protocol')
+  defaults = fetcher.get_label('com.chameth.proxy.default')
   for container, values in fetcher.get_label('com.chameth.proxy').items():
     networks = fetcher.get_networks(container)
     services.append({
       'port': values,
       'certificate': args.cert_path % domains[container][0],
       'trusted_certificate': args.trusted_cert_path % domains[container][0],
-      'certificate_key': args.cert_key_path % domains[container][0]
+      'certificate_key': args.cert_key_path % domains[container][0],
+      'default': container in defaults,
     })
 
   with open('/nginx-config/vhosts.conf', 'w') as f:

nginx.tpl

 {% for service in services %}
 server {
     server_name {{ ' '.join(service.vhosts) }};
-    listen [::]:443 ssl http2;
-    listen 443 ssl http2;
+    listen [::]:443{{ ' default_server' if default }} ssl http2;
+    listen 443{{ ' default_server' if default }} ssl http2;
 
     ssl_certificate {{ service.certificate }};
     ssl_trusted_certificate {{ service.trusted_certificate }};