bisect-kit: helper script to prepare source trees for ChromeOS bisection

Typical usage:

  Initial setup:
    $ setup_cros_bisect.py init --chromeos
    $ setup_cros_bisect.py init --chrome
    $ setup_cros_bisect.py init --android=pi-arc-dev

  Sync code if necessary:
    $ setup_cros_bisect.py sync

  Create source trees for bisection
    $ setup_cros_bisect.py new --session=12345

  After bisection finished, delete trees
    $ setup_cros_bisect.py delete --session=12345

BUG=None
TEST=run above commands

Change-Id: I6f94b57b9a2967addf6d654dd571a68b2d06e0d7
Reviewed-on: https://chromium-review.googlesource.com/1242666
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/cli.py b/bisect_kit/cli.py
index ba31246..26d125a 100644
--- a/bisect_kit/cli.py
+++ b/bisect_kit/cli.py
@@ -22,7 +22,6 @@
 
 logger = logging.getLogger(__name__)
 
-DEFAULT_SESSION_BASE = 'bisect.sessions'
 DEFAULT_SESSION_NAME = 'default'
 DEFAULT_CONFIDENCE = 0.999
 
@@ -578,7 +577,7 @@
     if not session:
       session = DEFAULT_SESSION_NAME
     if not session_base:
-      session_base = configure.get('SESSION_BASE', DEFAULT_SESSION_BASE)
+      session_base = configure.get('SESSION_BASE', common.DEFAULT_SESSION_BASE)
 
     session_file = os.path.join(session_base, session, self.domain_cls.__name__)
 
@@ -647,7 +646,7 @@
     common.add_common_arguments(parser)
     parser.add_argument(
         '--session_base',
-        default=configure.get('SESSION_BASE', DEFAULT_SESSION_BASE),
+        default=configure.get('SESSION_BASE', common.DEFAULT_SESSION_BASE),
         help='Directory to store sessions (default: %(default)r)')
     parser.add_argument(
         '--session',