Migrate from testr to stestr

* Replace .testr.conf by .stestr.conf for migration and update
  .gitignore accordingly
* Use py3 as the default runtime for tox and 3.18.0 as the
  minversion for tox

Change-Id: I5c389527c1e11ab9e1f5f5797cb1bd1e58bd8753

.gitignore

@@ -27,7 +27,7 @@ cover/
 !.coveragerc
 .tox
 nosetests.xml
-.testrepository
+.stestr/
 .venv
 
 # Translations

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=./security-analysis/tests/
+top_dir=./

.testr.conf

@@ -1,7 +0,0 @@
-[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 ./ . $LISTOPT $IDOPTION
-test_id_option=--load-list $IDFILE
-test_list_option=--list

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-minversion = 2.0
+minversion = 3.18.0
 envlist = docs
 skipsdist = True