Use a dedicated zuul launcher temp dir on /opt

When we download images, we use a lot of tmp space.  Rather than
writing them to the rood partition, which is not very large, use
the slightly larger /opt disk.

Change-Id: I6412a89890562728f4c5939065c0554f7698ff3e

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

@@ -14,3 +14,4 @@ services:
       - /home/zuuld:/home/zuul
       - /var/lib/zuul:/var/lib/zuul
       - /var/log/zuul:/var/log/zuul
+      - /opt/zuul-launcher-tmp:/opt/zuul-launcher-tmp

playbooks/roles/zuul-launcher/tasks/main.yaml

@@ -15,6 +15,14 @@
   vars:
     logrotate_file_name: /var/log/zuul/launcher-debug.log
 
+- name: Ensure launcher temp dir
+  file:
+    state: directory
+    path: /opt/zuul-launcher-tmp
+    mode: 0755
+    owner: "{{ zuul_user }}"
+    group: "{{ zuul_group }}"
+
 - name: Make docker-compose directory
   file:
     state: directory

playbooks/roles/zuul/templates/zuul.conf.j2

@@ -56,6 +56,7 @@ root=https://zuul.opendev.org
 
 [launcher]
 log_config=/etc/zuul/launcher-logging.conf
+temp_dir=/opt/zuul-launcher-tmp
 
 [auth local]
 driver=HS256