Invoke test_droid with -s for device serial number

The commandline changed slightly, and this is now required.  See
b/27301538.

Bug: 27376986
Test: Invoking test_droid like this manually works.

Change-Id: I58f9a4eb10faeb918f6f2bf5b37aa4a8e49e5a47
1 file changed
tree: 922fc124c8063f3e3c60984260b71f1a1ca4adf8
  1. .gitignore
  2. README.txt
  3. __init__.py
  4. builders/
  5. config_dump.json
  6. default.xml