Move BuilderStatus to lib/builder_status_lib

Going to move all operations on BuilderStatus to
lib/builder_status_lib. Firstly, move the BuilderStatus class to
lib/builder_status_lib in this CL.
With this change, manifest_version, build_status and relevant_changes
can import this module to access BuilderStatus, so they can avoid
circular dependency.

BUG=chromium:676452
TEST=unit_tests

Change-Id: I1da4bd45e9167a5b3011c71b0051bb00072301eb
Reviewed-on: https://chromium-review.googlesource.com/443072
Commit-Ready: Ningning Xia <nxia@chromium.org>
Tested-by: Ningning Xia <nxia@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 2dee1ac..a77a783 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -20,7 +20,6 @@
 import sys
 
 from chromite.cbuildbot import builders
-from chromite.cbuildbot import build_status
 from chromite.cbuildbot import cbuildbot_run
 from chromite.cbuildbot import remote_try
 from chromite.cbuildbot import repository
@@ -29,6 +28,7 @@
 from chromite.cbuildbot import tree_status
 from chromite.cbuildbot import trybot_patch_pool
 from chromite.cbuildbot.stages import completion_stages
+from chromite.lib import builder_status_lib
 from chromite.lib import cidb
 from chromite.lib import cgroups
 from chromite.lib import cleanup
@@ -1270,7 +1270,7 @@
       with open(options.mock_slave_status, 'r') as f:
         mock_statuses = pickle.load(f)
         for key, value in mock_statuses.iteritems():
-          mock_statuses[key] = build_status.BuilderStatus(**value)
+          mock_statuses[key] = builder_status_lib.BuilderStatus(**value)
       stack.Add(mock.patch.object,
                 completion_stages.MasterSlaveSyncCompletionStage,
                 '_FetchSlaveStatuses',