Debug env for tox

Running a test with pdb was difficult because testr captures
output and causes pdb prompt to quit.

Tips for how to run with debug are provided here:
 https://wiki.openstack.org/wiki/Testr#Debugging_.28pdb.29_Tests

This change puts these commands into a debug env in tox.ini so
you can do a command like

 tox -e debug test_v3_trust_token_get_token_fails

or, for more granularity:
 tox -e debug keystone.tests.test_sql_migrate_extensions.EndpointFilterExtension
 tox -e debug keystone.tests.test_sql_migrate_extensions.EndpointFilterExtension.test_downgrade

and when it hits your breakpoint you'll get the debug prompt.

Change-Id: I2b5dc81f4652dc89ecbcc7c785245a81cf77a1ca

tools/debug_helper.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+TMP_DIR=`mktemp -d` || exit 1
+trap "rm -rf $TMP_DIR" EXIT
+
+ALL_TESTS=$TMP_DIR/all_tests
+TESTS_TO_RUN=$TMP_DIR/ks_to_run
+
+python -m testtools.run discover -t ./ ./keystone/tests --list > $ALL_TESTS
+
+if [ "$1" ]
+then
+    grep "$1" < $ALL_TESTS > $TESTS_TO_RUN
+else
+    mv $ALL_TESTS $TESTS_TO_RUN
+fi
+
+STANDARD_THREADS=1 python -m testtools.run discover --load-list $TESTS_TO_RUN

tox.ini

@@ -27,6 +27,11 @@ commands = python setup.py testr --coverage --testr-args='{posargs}'
 [testenv:venv]
 commands = {posargs}
 
+[testenv:debug]
+
+commands =
+ {toxinidir}/tools/debug_helper.sh {posargs}
+
 [flake8]
 filename= *.py,keystone-*
 show-source = true