Enable strict coverage for step module

recipe_modules/step/tests/timeout.py

+# Copyright 2017 The LUCI Authors. All rights reserved.
+# Use of this source code is governed under the Apache License, Version 2.0
+# that can be found in the LICENSE file.
+
+from recipe_engine import recipe_api
+
+
+DEPS = [
+  'properties',
+  'step',
+]
+
+
+PROPERTIES = {
+  'timeout': recipe_api.Property(default=0, kind=int),
+}
+
+
+def RunSteps(api, timeout):
+  # Timeout causes the recipe engine to raise an exception if your step takes
+  # longer to run than you allow. Units are seconds.
+  try:
+    api.step('timeout', ['sleep', '20'], timeout=1)
+  except api.step.StepTimeout:
+    api.step('caught timeout', [])
+    raise
+
+
+def GenTests(api):
+  yield (
+      api.test('timeout') +
+      api.properties(timeout=1) +
+      api.step_data('timeout', times_out_after=20)
+    )