Fix a bug when paths is a string in find_files.

When test_paths is give as a path string the utils.find_files in
test_runner.py line 230 will return wrong list of file_list due to
this bug.

Test: run ACTs in the lab
Bug: 33492041
Change-Id: Ie2bbb19d1fd9ae242f8247923835e17f73e651fc
1 file changed
tree: 7713c160d653aa49dd2e0dcdb89cbba915bfc29e
  1. acts/
  2. Android.mk
  3. PREUPLOAD.cfg