init: restart celery workers on 'reload' (fixes #2904)

Sending HUP to the parent of a family of celery workers causes the
parent to re-exec itself, spawning a new set of child workers without
terminating the old ones.

So instead we send TERM to the parent on 'reload', which cleans up the
children, and rely on systemd/upstart to respawn the whole family.

etc/init/pandora-encoding.conf

@@ -7,6 +7,7 @@ start on runlevel [2345]
 stop on runlevel [!2345]
 
 respawn
+reload signal TERM
 
 env VENV=/srv/pandora
 env USER=pandora

etc/init/pandora-tasks.conf

@@ -7,6 +7,7 @@ start on runlevel [2345]
 stop on runlevel [!2345]
 
 respawn
+reload signal TERM
 
 env VENV=/srv/pandora
 env USER=pandora

etc/systemd/pandora-encoding.service

@@ -15,7 +15,7 @@ ExecStart=/srv/pandora/bin/python /srv/pandora/pandora/manage.py \
     -Q encoding -n pandora-encoding \
     --pidfile /run/pandora/encoding.pid \
     -l INFO
-ExecReload=/bin/kill -HUP $MAINPID
+ExecReload=/bin/kill -TERM $MAINPID
 
 [Install]
 WantedBy=multi-user.target

etc/systemd/pandora-tasks.service

@@ -15,7 +15,7 @@ ExecStart=/srv/pandora/bin/python /srv/pandora/pandora/manage.py \
     -Q default,celery -n pandora-default \
     --pidfile /run/pandora/tasks.pid \
     -l INFO
-ExecReload=/bin/kill -HUP $MAINPID
+ExecReload=/bin/kill -TERM $MAINPID
 
 [Install]
 WantedBy=multi-user.target