Update zuul-executor shutdown handling

We update the docker-compose config for zuul-executor to better handle
its shutdown handling. In particular we want to support zuul-executor
graceful which will pause the server then exit with rc 0 when all builds
complete. To do this we switch restart: always to restart: on-failure.
With the always setting docker simply restarts zuul-executor after a
graceful stop.

We also remove the stop signal of SIGHUP with its long timeout. Zuul
executor does not seem to catch SIGHUP for anything anymore so this is
there for old behavior and can be cleaned up.

Change-Id: I5211b91025ce5a13648f3648db3b42d357ecd590

playbooks/roles/zuul-executor/files/docker-compose.yaml

@@ -4,13 +4,11 @@ version: '2'
 
 services:
   executor:
-    restart: always
+    restart: on-failure
     image: docker.io/zuul/zuul-executor:latest
     network_mode: host
     user: zuul
     privileged: true
-    stop_signal: SIGHUP
-    stop_grace_period: 3h10m
     volumes:
       - /etc/zuul:/etc/zuul
       - /opt/project-config:/opt/project-config