Replace testrepository with stestr

Replace outdated testrepository with its newer sibling, which
is maintained.

Change-Id: I9755b82d8a2a82f146e71fdc0f32e3f6002e804d

.gitignore

@@ -2,6 +2,7 @@
 *.egg-info
 
 .tox
+.stestr
 build/*
 *.pyc
 gerritlib/versioninfo

.stestr.conf

@@ -0,0 +1,2 @@
+[DEFAULT]
+test_path=./gerritlib/tests

test-requirements.txt

@@ -1,4 +1,5 @@
 hacking>=0.5.6,<0.11
 sphinx>=1.1.2,<1.2
 python-subunit
-testrepository
+stestr<3.0.0;python_version<'3.5'
+stestr;python_version>='3.5'

tox.ini

@@ -6,11 +6,12 @@ skip_missing_interpreters = false
 envlist = pep8, py{38,37,36,35,27,py}
 
 [testenv]
-commands = python setup.py test --slowest --testr-args='{posargs}'
 setenv = VIRTUAL_ENV={envdir}
 usedevelop = True
 install_command = pip install {opts} {packages}
 deps = -r{toxinidir}/test-requirements.txt
+commands =
+    stestr run --slowest {posargs}
 
 [testenv:pep8]
 commands = flake8