[style] update python style to conform to PEP 8 (#3951)

With the exception of line length set to 119 vs. 79.

Add tests/ and tools/ to py-pretty-check.

tests/scripts/thread-cert/test_coaps.py

@@ -27,12 +27,9 @@
 #  POSSIBILITY OF SUCH DAMAGE.
 #
 
-import time
 import unittest
 
 import config
-import mle
-import network_layer
 import node
 
 LEADER = 1
@@ -40,7 +37,6 @@ ROUTER = 2
 
 
 class TestCoaps(unittest.TestCase):
-
     def setUp(self):
         self.simulator = config.create_default_simulator()
 
@@ -60,9 +56,9 @@ class TestCoaps(unittest.TestCase):
         self.nodes[ROUTER].set_router_selection_jitter(1)
 
     def tearDown(self):
-        for node in list(self.nodes.values()):
-            node.stop()
-            node.destroy()
+        for n in list(self.nodes.values()):
+            n.stop()
+            n.destroy()
         self.simulator.stop()
 
     def test(self):
@@ -86,7 +82,7 @@ class TestCoaps(unittest.TestCase):
         self.nodes[LEADER].coaps_stop()
 
         self.nodes[LEADER].coaps_start_x509()
-        #self.nodes[LEADER].coaps_set_resource_path('test')
+        # self.nodes[LEADER].coaps_set_resource_path('test')
         self.nodes[ROUTER].coaps_start_x509()
         self.nodes[ROUTER].coaps_connect(mleid)
         self.nodes[ROUTER].coaps_get()
@@ -94,5 +90,6 @@ class TestCoaps(unittest.TestCase):
         self.nodes[ROUTER].coaps_stop()
         self.nodes[LEADER].coaps_stop()
 
+
 if __name__ == '__main__':
     unittest.main()