fixed unit tests when env vars are set

Change-Id: Ia73c10c7c81b9434895941ea29282dbcdc667556

tests/unit/test_shell.py

@@ -387,6 +387,17 @@ class TestSubcommandHelp(unittest.TestCase):
 
 class TestParsing(unittest.TestCase):
 
+    def setUp(self):
+        super(TestParsing, self).setUp()
+        self._orig_environ = os.environ.copy()
+        keys = os.environ.keys()
+        for k in keys:
+            if k in ('ST_KEY', 'ST_USER', 'ST_AUTH'):
+                del os.environ[k]
+
+    def tearDown(self):
+        os.environ = self._orig_environ
+
     def _make_fake_command(self, result):
         def fake_command(parser, args, thread_manager):
             result[0], result[1] = swiftclient.shell.parse_args(parser, args)