[autotest] Mark slow unittests

These tests are "slow" because they start helper processes, taking
~0.10s each.  Thats too slow for unit test driven development, but
they are still useful tests.

BUG=chromium:748234
TEST=bin/test_lucifer
TEST=bin/test_lucifer --skipslow

Change-Id: I65db3627c3c50cba3ab403098e00e6c553a0cd70
Reviewed-on: https://chromium-review.googlesource.com/679212
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Paul Hobbs <phobbs@google.com>
diff --git a/venv/lucifer/conftest.py b/venv/lucifer/conftest.py
new file mode 100644
index 0000000..bc5176d
--- /dev/null
+++ b/venv/lucifer/conftest.py
@@ -0,0 +1,26 @@
+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""pytest extensions."""
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import pytest
+
+
+def pytest_addoption(parser):
+    """Add extra pytest options."""
+    parser.addoption("--skipslow", action="store_true",
+                     default=False, help="Skip slow tests")
+
+
+def pytest_collection_modifyitems(config, items):
+    """Modify tests to remove slow tests if --skipslow was passed."""
+    if config.getoption("--skipslow"):
+        skip_slow = pytest.mark.skip(reason="--skipslow option was passed")
+        for item in items:
+            if "slow" in item.keywords:
+                item.add_marker(skip_slow)