[Culprit-finder] Refactor findit testcase and move it to libs.

appengine/findit/model/flake/test/flake_analysis_request_test.py

Index: appengine/findit/model/flake/test/flake_analysis_request_test.py
diff --git a/appengine/findit/model/flake/test/flake_analysis_request_test.py b/appengine/findit/model/flake/test/flake_analysis_request_test.py
index e6876a34d287f25201fd165a59a3a08870667fc1..bb99e02c04ba0ebf88c441cd7a10982503e981e3 100644
--- a/appengine/findit/model/flake/test/flake_analysis_request_test.py
+++ b/appengine/findit/model/flake/test/flake_analysis_request_test.py
@@ -5,13 +5,13 @@
 from datetime import datetime
 import mock
 
-from common.findit_testcase import FinditTestCase
+from libs.testcase import TestCase
 from model.flake.flake_analysis_request import BuildStep
 from model.flake.flake_analysis_request import FlakeAnalysisRequest
 from model.flake.master_flake_analysis import MasterFlakeAnalysis
 
 
-class FlakeAnalysisRequestTest(FinditTestCase):
+class FlakeAnalysisRequestTest(TestCase):
 
   def testStripMasterPrefix(self):
     cases = {