Add .stestr.conf to manage default OS_TEST_PATH

... following the pattern found in the other repos.

Change-Id: I4816aee9d82cdfc7d2101057226d95a1d7c85695
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=${OS_TEST_PATH:-./observabilityclient/tests/unit}
+top_dir=./

tox.ini

@@ -4,8 +4,6 @@ envlist = py3,pep8
 
 [testenv]
 usedevelop = True
-setenv =
-  OS_TEST_PATH = ./observabilityclient/tests/unit
 passenv =
   PROMETHEUS_*
   OBSERVABILITY_*
@@ -13,7 +11,7 @@ deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
-commands = stestr run --slowest --test-path {env:OS_TEST_PATH} {posargs}
+commands = stestr run --slowest {posargs}
 
 [testenv:pep8]
 skip_install = true
@@ -27,8 +25,7 @@ commands = {posargs}
 
 [testenv:cover]
 setenv =
-    {[testenv]setenv}
-    PYTHON=coverage run --source observabilityclient --parallel-mode
+  PYTHON=coverage run --source observabilityclient --parallel-mode
 commands =
   coverage erase
   {[testenv]commands}