Migrate testr to stestr

Note that the interface doesn't have any unit tests yet.

Change-Id: I91bfe767e7d10b696a73c7141dbefe8ec30e297c

.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

@@ -1,5 +1,5 @@
 [tox]
-envlist = pep8,py34,py35
+envlist = pep8,py35
 skipsdist = True
 # NOTE(beisner): Avoid build/test env pollution by not enabling sitepackages.
 sitepackages = False
@@ -11,16 +11,16 @@ setenv = VIRTUAL_ENV={envdir}
          PYTHONHASHSEED=0
 install_command =
   pip install {opts} {packages}
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
-[testenv:py34]
-basepython = python3.4
+[testenv:py35]
+basepython = python3.5
 deps = -r{toxinidir}/test-requirements.txt
 # TODO: Need to write unit tests then remove the following command.
 commands = /bin/true
 
-[testenv:py35]
-basepython = python3.5
+[testenv:py3]
+basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
 # TODO: Need to write unit tests then remove the following command.
 commands = /bin/true