Add pretty_tox.sh wrapper script to use subunit-trace

This commit adds a pretty_tox.sh wrapper script for the tempest-lib
unit tests to use subunit-trace when running the tests. This should
make the output a bit more clear and help with future debugging.

Change-Id: I48d670353bb85f7f87a05041bed60ad131555057

tools/pretty_tox.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+set -o pipefail
+
+TESTRARGS=$1
+python setup.py testr --slowest --testr-args="--subunit $TESTRARGS" | subunit-trace --no-failure-debug -f

tox.ini

@@ -6,11 +6,12 @@ skipsdist = True
 [testenv]
 usedevelop = True
 install_command = pip install -U {opts} {packages}
+whitelist_externals = bash
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = python setup.py testr --slowest --testr-args='{posargs}'
+commands = bash tools/pretty_tox.sh {posargs}
 
 [testenv:pep8]
 commands = flake8