Rename constants

BUG=chromium:703769
TEST=None

Change-Id: I726c3917806a88e8913cf14e7b2835f8041f09f3
diff --git a/cros_venv/constants.py b/cros_venv/constants.py
index 18cdb95..3292ac0 100644
--- a/cros_venv/constants.py
+++ b/cros_venv/constants.py
@@ -23,5 +23,8 @@
 
 import cros_venv
 
-PACKAGE_DIR = os.path.abspath(cros_venv.__path__[0])
-WORKTREE_DIR = os.path.dirname(PACKAGE_DIR)
+# Directory of cros_venv package
+_CROS_VENV_DIR = os.path.abspath(cros_venv.__path__[0])
+
+# Root directory of infra_virtualenv repo
+REPO_DIR = os.path.dirname(_CROS_VENV_DIR)
diff --git a/cros_venv/venvlib.py b/cros_venv/venvlib.py
index bc2967a..04460d6 100644
--- a/cros_venv/venvlib.py
+++ b/cros_venv/venvlib.py
@@ -17,7 +17,7 @@
 from cros_venv import constants
 from cros_venv import flock
 
-_PACKAGE_DIR = os.path.join(constants.WORKTREE_DIR, 'pip_packages')
+_PACKAGE_DIR = os.path.join(constants.REPO_DIR, 'pip_packages')
 _VENV_PY = '/usr/bin/python2.7'
 
 # BASE_DEPENDENCIES are pip requirements automatically included in every