Migrate unit tests from testr to stestr

Note: there aren't actually any unit tests, but this at least moves it
away from the deprecated library.

Change-Id: Ic9bec4534bc200d427241cd60b5b90b0fd89102e

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=./unit_tests
+top_dir=./

test-requirements.txt

@@ -1,2 +1,2 @@
-flake8>=2.2.4,<=2.4.1
-os-testr>=0.4.1
+flake8>=2.2.4
+stestr>=2.2.0

tox.ini

@@ -11,7 +11,7 @@ setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
 install_command =
   pip install {opts} {packages}
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
 [testenv:py34]
 basepython = python3.4
@@ -25,6 +25,12 @@ deps = -r{toxinidir}/test-requirements.txt
 # TODO: Need to write unit tests then remove the following command.
 commands = /bin/true
 
+[testenv:py3]
+basepython = python3
+deps = -r{toxinidir}/test-requirements.txt
+# TODO: Need to write unit tests then remove the following command.
+commands = /bin/true
+
 [testenv:pep8]
 basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
@@ -35,4 +41,4 @@ basepython = python3
 commands = {posargs}
 
 [flake8]
-ignore = E402,E226
+ignore = E402,E226,W504,W503