bisect-kit: extract common variable, BISECT_KIT_ROOT

BUG=None
TEST=unittest

Change-Id: Ie87818b486f9f39d9a3b833b3af3f20d9d8795ea
Reviewed-on: https://chromium-review.googlesource.com/1521853
Commit-Ready: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Chung-yih Wang <cywang@chromium.org>
diff --git a/bisect_kit/configure_test.py b/bisect_kit/configure_test.py
index 4a482ff..bcee2fe 100644
--- a/bisect_kit/configure_test.py
+++ b/bisect_kit/configure_test.py
@@ -14,6 +14,7 @@
 
 import mock
 
+from bisect_kit import common
 from bisect_kit import configure
 
 
@@ -118,7 +119,7 @@
 
   def test_load_sample_config(self):
     filename = 'bisect_kit.json.sample'
-    path = os.path.join(os.path.dirname(__file__), '..', filename)
+    path = os.path.join(common.BISECT_KIT_ROOT, filename)
     config = configure.ConfigStore(path)
 
     # Load succeeded, no exceptions.