set app user home dir environment variable

by default supervisord only switches user, but keeps environment untouched. this results in $HOME var pointing to /root where
 app user has no access. this break some apps, notably pip install.

Author: scorpp

supervisor.ini

@@ -4,7 +4,7 @@ nodaemon = true
 [program:wsgi]
 user = app
 command = /home/app/start-gunicorn.sh
-environment=PATH="/srv/virtenv/bin:%(ENV_PATH)s"
+environment=PATH="/srv/virtenv/bin:%(ENV_PATH)s",HOME="/home/app"
 autorestart = false
 startretries=0
 stdout_events_enabled = true