[style] apply google python style guide (#4501)

This commit applies and enforces Google's python style for tests.

tests/scripts/thread-cert/test_coaps.py

@@ -37,6 +37,7 @@ ROUTER = 2
 
 
 class TestCoaps(unittest.TestCase):
+
     def setUp(self):
         self.simulator = config.create_default_simulator()