Tweak the default acccess log format

Make sure we've got the most important information like remote addr,
request status line, response code, response size, user agent and
request processing time, e.g:

    [10/Jan/2018:21:04:46 +0000] 127.0.0.1 "GET /snippets/42/raw HTTP/1.1" 200 154 "curl/7.54.0" 0.100991

Note, that for production deploys behind a reverse-proxy this format
might be changed to use the HTTP headers like X-Real-IP or
X-Forwarded-For, if needed.

Author: malor

xsnippet/web_backend/__main__.py

@@ -12,4 +12,9 @@
 
 # create an app instance and listen forever
 app = create_app(conf)
-aiohttp.web.run_app(app, host=conf.LISTEN_HOST, port=conf.LISTEN_PORT)
+aiohttp.web.run_app(
+    app,
+    host=conf.LISTEN_HOST,
+    port=conf.LISTEN_PORT,
+    access_log_format=conf.ACCESS_LOG_FORMAT
+)

xsnippet/web_backend/conf.py

@@ -5,3 +5,5 @@
 
 LISTEN_HOST = os.environ.get('XSNIPPET_WEB_PROXY_HOST', '0.0.0.0')
 LISTEN_PORT = os.environ.get('XSNIPPET_WEB_PROXY_PORT', 5000)
+
+ACCESS_LOG_FORMAT = '%t %a "%r" %s %b "%{User-Agent}i" %Tf'