Unit test of script hook

This test asserts the following when the script hook is invoked
with test data:
- Expected env variables are set
- Script contents matches the fake config tool contents
- Script is invoked with no arguments
- Written output files result in output values being set
- Script responding with a failure returncode propagates to the
  response

Change-Id: I1c32ec89b1ce16c25e3a29ab36e016cca5ff7835
Merge "Unit test of script hook"