build: Call 'systemd-tmpfiles --create' when installing

It's only necessary to call 'systemd-tmpfiles --create' when building
and installing from source, and not when using a pre-built binary
downstream package, because:

  * When 'meson install' is called as part of building the package,
    that's not when the temporary files need to be created. They need
    to be created when the binary package is later downloaded and
    installed by the user.

  * Downstream tools can sometimes handle it automatically. eg., on
    Fedora, the systemd RPM installs a trigger that tells RPM to call
    'systemd-tmpfiles --create' automatically when a tmpfiles.d snippet
    is installed.

Downstream distributors set the DESTDIR environment variable when
building their packages. Therefore, it's used to detect when a
downstream package is being built.

containers#955

meson.build

@@ -65,3 +65,5 @@ subdir('data')
 subdir('doc')
 subdir('profile.d')
 subdir('src')
+
+meson.add_install_script('meson_post_install.py')

meson_post_install.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python3
+
+import os
+import subprocess
+
+destdir = os.environ.get('DESTDIR', '')
+
+if not destdir and not os.path.exists('/run/.containerenv'):
+    print('Calling systemd-tmpfiles --create ...')
+    subprocess.call(['systemd-tmpfiles', '--create'])

playbooks/setup-env.yaml

@@ -52,10 +52,3 @@
       args:
         chdir: '{{ zuul.project.src_dir }}'
         creates: /usr/local/bin/toolbox
-
-    - name: Setup environment
-      become: yes
-      command:
-        cmd: systemd-tmpfiles --create
-        creates: /run/media
-        creates: /run/host