bisect-kit: fix pylint errors

Besides normal fixes, BisectorCommandLineInterface is renamed to
BisectorCommandLine. Although new version of pylint no longer complain
interface-not-implemented (instead, saying the disable option is
undefined), chromite and depot_tools still use the old one. Renaming is
easier to avoid the annoyingness.

BUG=chromium:776314
TEST=cros lint *.py bisect_kit/*.py

Change-Id: I4cf3f63ee950d913a6b3f5b6a7a7b59810066963
Reviewed-on: https://chromium-review.googlesource.com/987660
Commit-Ready: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Kuang-che Wu <kcwu@chromium.org>
diff --git a/bisect_kit/git_util.py b/bisect_kit/git_util.py
index 0c8e51f..9868328 100644
--- a/bisect_kit/git_util.py
+++ b/bisect_kit/git_util.py
@@ -100,7 +100,7 @@
   return msg
 
 
-def get_commit_hash(git_root, rev):
+def get_commit_hash(git_repo, rev):
   """Get git commit hash.
 
   Args:
@@ -111,6 +111,6 @@
     full git commit hash
   """
   cmd = ['git', 'rev-parse', rev]
-  git_rev = util.check_output(*cmd, cwd=git_root).strip()
+  git_rev = util.check_output(*cmd, cwd=git_repo).strip()
   assert git_rev
   return git_rev