[autotest] Add import path hack for moblab

This is needed for Moblab because dependencies are installed
system-wide instead of using build_externals.py.

BUG=chromium:800492
TEST=None

Change-Id: I792376016f9ffece506c457c1fd898f151ed876c
Reviewed-on: https://chromium-review.googlesource.com/887625
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1043209
Reviewed-by: Keith Haddow <haddowk@chromium.org>
Commit-Queue: Keith Haddow <haddowk@chromium.org>
Tested-by: Keith Haddow <haddowk@chromium.org>
diff --git a/venv/lucifer/autotest.py b/venv/lucifer/autotest.py
index 60f984e..e606e79 100644
--- a/venv/lucifer/autotest.py
+++ b/venv/lucifer/autotest.py
@@ -120,6 +120,18 @@
     return ast.literal_eval(output)
 
 
+def _system_site_packages():
+    """Get list of system site-package directories.
+
+    This is needed for Moblab because dependencies are installed
+    system-wide instead of using build_externals.py.
+    """
+    output = subprocess.check_output([
+        _SYSTEM_PYTHON, '-c',
+        'import site; print repr(site.getsitepackages())'])
+    return ast.literal_eval(output)
+
+
 class _CommonRemovingFinder(object):
     """Python import finder that neuters Autotest's common.py