Switch to testr serial instead of nose

This commit removes all usage of nose from tox and run_tests.sh and
migrates over to testr for running tests serially.

Change-Id: I484e02f24d3b30d976860b69d26f3276775deddc
diff --git a/tools/pretty_tox_serial.sh b/tools/pretty_tox_serial.sh
index 490d263..dd7b682 100755
--- a/tools/pretty_tox_serial.sh
+++ b/tools/pretty_tox_serial.sh
@@ -5,5 +5,5 @@
 if [ ! -d .testrepository ]; then
     testr init
 fi
-testr run --subunit $TESTRARGS | subunit-2to1 | tools/colorizer.py
+testr run --subunit $TESTRARGS | subunit2pyunit
 testr slowest