test: Various mkosi integration test improvements

- Stop using logging module since the default output formatting is
  pretty bad. Prefer print() for now.
- Log less, logging the full mkosi command line is rather verbose,
  especially when it contains multi-line dropins.
- Streamline the journalctl command we output for debugging failed
  tests.
- Don't force usage of the disk image format.
- Don't force running without unit tests.
- Don't force disabling RuntimeBuildSources.
- Update documentation to streamline the command for running a single
  test and remove sudo as it's not required anymore.
- Improve the console output by having the test unit's output logged
  to both the journal and the console.
- Disable journal console log forwarding as we have journal forwarding
  as a better alternative.
- Delete existing journal file before running test.
- Delete journal files of succeeded tests to reduce disk usage.
- Rename system_mkosi target to just mkosi
- Pass in mkosi source directory explicitly to accomodate arbitrary
  build directory locations.
- Add test interactive debugging if stdout is connected to a tty
- Stop explicitly using the 'system' image since it'll likely be
  dropped soon.
- Only forward journal if we're not running in debugging mode.
- Stop using testsuite.target and instead just add the necessary
  extras to the main testsuite unit via the credential dropin.
- Override type to idle so test output is not interleaved with
  status output.
- Don't build mkosi target by default
- Always add the mkosi target if mkosi is found
- Remove dependency of the integration tests on the mkosi target
  as otherwise the image is always built, even though we configure
  it to not be built by default.
- Move mkosi output, cache and build directory into build/ so that
  invocations from meson and regular invocations share the same
  directories.
- Various aesthetic cleanups.

test/integration-test-wrapper.py

@@ -0,0 +1,130 @@
+#!/usr/bin/python3
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+'''Test wrapper command for driving integration tests.
+
+Note: This is deliberately rough and only intended to drive existing tests
+with the expectation that as part of formally defining the API it will be tidy.
+
+'''
+
+import argparse
+import os
+import shlex
+import subprocess
+import sys
+import textwrap
+from pathlib import Path
+
+
+EMERGENCY_EXIT_DROPIN = """\
+[Unit]
+Wants=emergency-exit.service
+"""
+
+
+EMERGENCY_EXIT_SERVICE = """\
+[Unit]
+DefaultDependencies=no
+Conflicts=shutdown.target
+Conflicts=rescue.service
+Before=shutdown.target
+Before=rescue.service
+FailureAction=exit
+
+[Service]
+ExecStart=false
+"""
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument('--meson-source-dir', required=True, type=Path)
+    parser.add_argument('--meson-build-dir', required=True, type=Path)
+    parser.add_argument('--test-name', required=True)
+    parser.add_argument('--test-number', required=True)
+    parser.add_argument('mkosi_args', nargs="*")
+    args = parser.parse_args()
+
+    test_unit = f"testsuite-{args.test_number}.service"
+
+    dropin = textwrap.dedent(
+        """\
+        [Unit]
+        After=multi-user.target network.target
+        Requires=multi-user.target
+
+        [Service]
+        StandardOutput=journal+console
+        """
+    )
+
+    if not sys.stderr.isatty():
+        dropin += textwrap.dedent(
+            """
+            [Unit]
+            SuccessAction=exit
+            FailureAction=exit
+            """
+        )
+
+        journal_file = (args.meson_build_dir / (f"test/journal/{args.test_name}.journal")).absolute()
+        journal_file.unlink(missing_ok=True)
+    else:
+        journal_file = None
+
+    cmd = [
+        'mkosi',
+        '--directory', os.fspath(args.meson_source_dir),
+        '--output-dir', os.fspath(args.meson_build_dir / 'mkosi.output'),
+        '--extra-search-path', os.fspath(args.meson_build_dir),
+        '--machine', args.test_name,
+        '--ephemeral',
+        *(['--forward-journal', journal_file] if journal_file else []),
+        *(
+            [
+                '--credential',
+                f"systemd.extra-unit.emergency-exit.service={shlex.quote(EMERGENCY_EXIT_SERVICE)}",
+                '--credential',
+                f"systemd.unit-dropin.emergency.target={shlex.quote(EMERGENCY_EXIT_DROPIN)}",
+                '--kernel-command-line-extra=systemd.mask=serial-getty@.service',
+            ]
+            if not sys.stderr.isatty()
+            else []
+        ),
+        '--credential',
+        f"systemd.unit-dropin.{test_unit}={shlex.quote(dropin)}",
+        '--append',
+        '--kernel-command-line-extra',
+        ' '.join([
+            'systemd.hostname=H',
+            f"SYSTEMD_UNIT_PATH=/usr/lib/systemd/tests/testdata/testsuite-{args.test_number}.units:/usr/lib/systemd/tests/testdata/units:",
+            f"systemd.unit={test_unit}",
+        ]),
+        *args.mkosi_args,
+        'qemu',
+    ]
+
+    try:
+        subprocess.run(cmd, check=True)
+    except subprocess.CalledProcessError as e:
+        if e.returncode != 77 and journal_file:
+            cmd = [
+                'journalctl',
+                '--no-hostname',
+                '-o', 'short-monotonic',
+                '--file', journal_file,
+                '-u', test_unit,
+                '-p', 'info',
+            ]
+            print("Test failed, relevant logs can be viewed with: \n\n"
+                  f"{shlex.join(str(a) for a in cmd)}\n", file=sys.stderr)
+        exit(e.returncode)
+
+    # Do not keep journal files for tests that don't fail.
+    if journal_file:
+        journal_file.unlink(missing_ok=True)
+
+
+if __name__ == '__main__':
+    main()