s3/test: nuke tempdir but keep $tempdir/log

before this change, if the object_store test fails, the tempdir
will be preserved. and if our CI test pipeline is used to perform
the test, the test job would scan for the artifacts, and if the
test in question fails, it would take over 1 hour to scan the tempdir.

to alleviate the pain, let's just keep the scylla logging file
no matter the test fails or succeeds. so that jenkins can scan the
artifacts faster if the test fails.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes #14880

test/object_store/conftest.py

@@ -45,28 +45,29 @@ def ssl(request):
     yield request.config.getoption('--ssl')
 
 
-@contextmanager
-def _maybe_remove_tempdir_on_complete(request, tempdir):
-    if pytest.version_tuple > (7, 3, 0):
-        yield
+def _remove_all_but(tempdir, to_preserve):
+    orig_fn = os.path.join(tempdir, to_preserve)
+    # orig_fn does not exist
+    if not os.path.exists(orig_fn):
+        # it's fine if tempdir does not exist
+        shutil.rmtree(tempdir=True)
         return
-    # tmp_path_retention_count was introduced in pytest 7.3.0, so we have
-    # to swing this by ourselves when using lower version of pytest. see
-    # https://docs.pytest.org/en/7.3.x/changelog.html#pytest-7-3-0-2023-04-08
-    tests_failed = request.session.testsfailed
-    yield
-    if tests_failed == request.session.testsfailed:
-        # not tests failed after this seesion, so remove the tempdir
+
+    with tempfile.TemporaryDirectory() as backup_tempdir:
+        backup_fn = os.path.join(backup_tempdir, to_preserve)
+        shutil.move(orig_fn, backup_fn)
         shutil.rmtree(tempdir)
+        os.mkdir(tempdir)
+        shutil.move(backup_fn, orig_fn)
 
 
 @pytest.fixture(scope="function")
-def test_tempdir(request, tmpdir):
+def test_tempdir(tmpdir):
     tempdir = tmpdir.strpath
-    with _maybe_remove_tempdir_on_complete(request, tempdir):
+    try:
         yield tempdir
-        with open(os.path.join(tempdir, 'log'), 'rb') as log:
-            shutil.copyfileobj(log, sys.stdout.buffer)
+    finally:
+        _remove_all_but(tempdir, 'log')
 
 
 @pytest.fixture(scope="function")