Set pipefail for wrapper scripts

Previously if the testr list command was failing subunit2py would
return a 0 making the test runs that use the pretty_tox scripts also
return 0 despite testr actually failing. This commit gets around this
condition by setting pipefail in the pretty_tox scripts to ensure that
we actually fail.

Change-Id: I9cbaf83cfea7c02133b27fe639e7ea12edb48f7e
4 files changed