Replace ostestr with stestr in testing framework.

A system upgrade broke ostestr. We can fix it by just calling stestr
directly.

Change-Id: Iefa4a23d02aca71b6b1aba6c4369a11c054e92fa

.stestr.conf

+[DEFAULT]
+test_path=./unit_tests
+top_dir=./

.testr.conf

-[DEFAULT]
-test_command=OS_STDOUT_CAPTURE=${OS_STDOUT_CAPTURE:-1} \
-             OS_STDERR_CAPTURE=${OS_STDERR_CAPTURE:-1} \
-             OS_TEST_TIMEOUT=${OS_TEST_TIMEOUT:-60} \
-             ${PYTHON:-python} -m subunit.run discover -t ./ ./unit_tests $LISTOPT $IDOPTION
-
-test_id_option=--load-list $IDFILE
-test_list_option=--list

src/test-requirements.txt

@@ -5,7 +5,7 @@ charm-tools>=2.4.4
 coverage>=3.6
 mock>=1.2
 flake8>=2.2.4,<=2.4.1
-os-testr>=0.4.1
+stestr>=2.2.0
 requests>=2.18.4
 # BEGIN: Amulet OpenStack Charm Helper Requirements
 # Liberty client lower constraints

test-requirements.txt

@@ -4,7 +4,7 @@
 #
 # Lint and unit test requirements
 flake8>=2.2.4,<=2.4.1
-os-testr>=0.4.1
+stestr>=2.2.0
 requests>=2.18.4
 charms.reactive
 mock>=1.2

tox.ini

@@ -47,22 +47,22 @@ commands = true
 [testenv:py3]
 basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
 [testenv:py34]
 basepython = python3.4
 deps = -r{toxinidir}/test-requirements.txt
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
 [testenv:py35]
 basepython = python3.5
 deps = -r{toxinidir}/test-requirements.txt
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
 [testenv:py36]
 basepython = python3.6
 deps = -r{toxinidir}/test-requirements.txt
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
 [testenv:pep8]
 basepython = python3
@@ -80,7 +80,7 @@ setenv =
     PYTHON=coverage run
 commands =
     coverage erase
-    ostestr {posargs}
+    stestr run {posargs}
     coverage combine
     coverage html -d cover
     coverage xml -o cover/coverage.xml