Use testr for running functional tests and documentation

Alters tox.ini to use testr rather than nosetests.
Also, adds documentation on how to use tox to run a
single functional test class.

Change-Id: I1333ead397f338ee3da3d81b0e1de8e93283a2b5
Closes-Bug: #1490747

tox.ini

@@ -57,10 +57,10 @@ commands=
 [testenv:functional]
 # This tox env is purely to make local test development easier
 # Note: This requires local running instances of Barbican and Keystone
-deps =
-    {[testenv]deps}
-    nose
-commands = nosetests -v --processes=-1 --process-timeout=600 {toxinidir}/functionaltests {posargs}
+deps = -r{toxinidir}/test-requirements.txt
+setenv = OS_TEST_PATH={toxinidir}/functionaltests
+commands =
+    /bin/bash {toxinidir}/functionaltests/pretty_tox.sh '{posargs}'
 
 [flake8]
 # E711 ignored because of sqlalchemy override of == None