Change default job_dir location

To increase the chances that job_dir and git_dir are on the
same filesystem in the default configuration, set the default
job_dir to /var/lib/zuul/builds.

Also, all zuul container images specify a volume at /var/lib/zuul,
therefore the docker-compose file does not need to specify the
same for the scheduler container.

Due to this, we were inadvertently running the executor with the
git_dir and job_dir on different filesystems in the quick-start.
That should no longer be the case.

Change-Id: I2fe5eea588006da7181c3ea8ad2637598764e8f1

doc/source/admin/components.rst

@@ -529,7 +529,7 @@ The following sections of ``zuul.conf`` are used by the executor:
       cache.
 
    .. attr:: job_dir
-      :default: /tmp
+      :default: /var/lib/zuul/builds
 
       Directory that Zuul should use to hold temporary job directories.
       When each job is run, a new entry will be created under this

doc/source/admin/examples/docker-compose.yaml

@@ -54,7 +54,6 @@ services:
       - "./etc_zuul/:/etc/zuul/:z"
       - "./playbooks/:/var/playbooks/:z"
       - "sshkey:/var/ssh:z"
-      - /var/lib/zuul
   web:
     command: "sh -c '/var/playbooks/wait-to-start-gearman.sh && zuul-web -d'"
     depends_on:

releasenotes/notes/jobdir_default-991bd60141045b68.yaml

@@ -0,0 +1,13 @@
+---
+upgrade:
+  - |
+    The default value for the :attr:`executor.job_dir` configuration
+    setting has been changed from ``/tmp`` to
+    ``/var/lib/zuul/builds``.  It is important for
+    :attr:`executor.job_dir` and :attr:`executor.git_dir` to be
+    located on the same filesystem, so this change increases the chances
+    that they end up on the same filesystem in most default configurations.
+
+    The ``builds`` subdirectory will be created if it does not exist,
+    however, ``/var/lib/zuul`` at least must exist and be writable by
+    the Zuul user.

zuul/cmd/executor.py

@@ -18,7 +18,6 @@ import logging
 import os
 import sys
 import signal
-import tempfile
 
 import zuul.cmd
 import zuul.executor.server
@@ -86,7 +85,9 @@ class Executor(zuul.cmd.ZuulDaemonApp):
                     job_dir=self.job_dir))
                 sys.exit(1)
         else:
-            self.job_dir = tempfile.mkdtemp()
+            self.job_dir = '/var/lib/zuul/builds'
+            if not os.path.exists(self.job_dir):
+                os.mkdir(self.job_dir)
 
         self.setup_logging('executor', 'log_config')
         self.log = logging.getLogger("zuul.Executor")