Add pdb support to tox with debug helper shell script

The Keystone team has been using a home brewed `debug_helper.sh`
file to run tests with pdb support, it's now being also used by
pycadf too. As noted by bnemec [1] we should move this to oslo.
[1] https://bugs.launchpad.net/pycadf/+bug/1354192

To run any test in particular, run tox with -e debug:
  `tox -e debug`

It also supports passing in a specific test module, class or case.
The shell file runs testtools underneath the covers to get pdb
support.

Change-Id: Idb715bc137459a2f6d16ac3f65c718a567df49ff
Co-Authored-By: Brant Knudson <bknudson@us.ibm.com>

setup.cfg

@@ -22,6 +22,8 @@ classifier =
 [files]
 packages =
     oslotest
+scripts =
+    tools/oslo_debug_helper.sh
 
 [global]
 setup-hooks =

tools/oslo_debug_helper.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+
+# To utilize this file, add the following to tox.ini:
+#[testenv:debug]
+#commands = oslo_debug_helper.sh {posargs}
+
+# To run with tox:
+#tox -e debug
+#tox -e debug test_notifications
+#tox -e debug test_notifications.NotificationsTestCase
+#tox -e debug test_notifications.NotificationsTestCase.test_send_notification
+
+TMP_DIR=`mktemp -d` || exit 1
+trap "rm -rf $TMP_DIR" EXIT
+
+ALL_TESTS=$TMP_DIR/all_tests
+TESTS_TO_RUN=$TMP_DIR/tests_to_run
+
+PACKAGENAME=$(python setup.py --name)
+
+python -m testtools.run discover -t ./ ./$PACKAGENAME/tests --list > $ALL_TESTS
+
+if [ "$1" ]; then
+    grep "$1" < $ALL_TESTS > $TESTS_TO_RUN
+else
+    mv $ALL_TESTS $TESTS_TO_RUN
+fi
+
+python -m testtools.run discover --load-list $TESTS_TO_RUN
+