test: Skip meson integration tests if SYSTEMD_INTEGRATION_TESTS != 1

We cannot mark a test suite as excluded by default in meson. Instead,
let's require that SYSTEMD_INTEGRATION_TESTS=1 and skip any integration
test if it's not set. This is effectively the same as excluding it by
default. If the integration-test option is enabled, we'll set the
environment variable by default, just like we do with SYSTEMD_SLOW_TESTS
and the slow-tests meson option.

test/integration-test-wrapper.py

@@ -38,6 +38,10 @@ ExecStart=false
 
 
 def main():
+    if not bool(int(os.getenv("SYSTEMD_INTEGRATION_TESTS", "0"))):
+        print("SYSTEMD_INTEGRATION_TESTS=1 not found in environment, skipping", file=sys.stderr)
+        exit(77)
+
     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)