Docker: generate our own log config

When running under docker, we want to use docker's own logging stuff rather
than losing the logs somewhere on the container's filesystem, so let's use log
configs that spit logs out to stdout instead.

docker/start.py

@@ -116,9 +116,16 @@ def run_generate_config(environ, ownership):
         if v not in environ:
             error("Environment variable '%s' is mandatory in `generate` mode." % (v,))
 
+    server_name = environ["SYNAPSE_SERVER_NAME"]
     config_dir = environ.get("SYNAPSE_CONFIG_DIR", "/data")
     data_dir = environ.get("SYNAPSE_DATA_DIR", "/data")
 
+    # create a suitable log config from our template
+    log_config_file = "%s/%s.log.config" % (config_dir, server_name)
+    if not os.path.exists(log_config_file):
+        log("Creating log config %s" % (log_config_file,))
+        convert("/conf/log.config", log_config_file, environ)
+
     # make sure that synapse has perms to write to the data dir.
     subprocess.check_output(["chown", ownership, data_dir])
 
@@ -127,7 +134,7 @@ def run_generate_config(environ, ownership):
         "-m",
         "synapse.app.homeserver",
         "--server-name",
-        environ["SYNAPSE_SERVER_NAME"],
+        server_name,
         "--report-stats",
         environ["SYNAPSE_REPORT_STATS"],
         "--config-path",