docker_registry.run: Restore GUNICORN_OPTS functionality

This was initially added in 534c6da (run.sh: Add '$GUNICORN_OPTS
"$@"' to gunicorn invocation, 2014-02-13), but didn't survive the
translation to a setuptools entry_points in bf3360a (replacing run.sh
with a "docker-registry" console script, 2014-04-02).  bf3360a was
part of #297, which branched off before
534c6da landed with #247, and the
entry_points invocation wasn't updated to reflect the change.

The syntax has also changed a bit, since we're invoking Gunicorn from
Python instead of Bash.  Instead of dropping the string verbatim onto
the command-line ($GUNICORN_OPTS), it now goes through the usual
docker_registry.server.env.source YAML parsing (884b418, Type from
environment properly (like Config), 2014-06-23).  So instead of
something like:

  GUNICORN_OPTS='--preload --log-syslog'

you should now be using:

  GUNICORN_OPTS='[--preload, --log-syslog]'

Author: wking

docker_registry/run.py

@@ -77,6 +77,7 @@ def run_gunicorn():
         '-t', env.source('GUNICORN_SILENT_TIMEOUT'),
         '-w', env.source('GUNICORN_WORKERS'),
         '-b', address,
+    ] + env.source('GUNICORN_OPTS') + [
         'docker_registry.wsgi:application'
     ]
 

docker_registry/server/env.py

@@ -13,7 +13,8 @@
     'GUNICORN_GRACEFUL_TIMEOUT': '3600',
     'GUNICORN_SILENT_TIMEOUT': '3600',
     'GUNICORN_ACCESS_LOG_FILE': '"-"',
-    'GUNICORN_ERROR_LOG_FILE': '"-"'
+    'GUNICORN_ERROR_LOG_FILE': '"-"',
+    'GUNICORN_OPTS': '[]',
 }