fix: what bandit and the remaining lint rules found

- nosec for SHA512_password in the login payload (B105): it is a flag
  telling the gateway how Input_Passwd is encoded, not a password; a false
  positive.
- A failed login raises ConnectionException from the underlying error, so
  the cause stays attached.
- tests: pytest.raises instead of try / assert False / except, which
  python -O would have turned into tests that always pass.

tests/test_zyxel.py

@@ -146,11 +146,8 @@ class TestZyxelVMGDriver:
                 sess = MagicMock()
                 sess.get.side_effect = requests.ConnectionError("unreachable")
                 mock_session.return_value = sess
-                try:
+                with pytest.raises(ConnectionException):
                     self.driver.open()
-                    assert False, "Expected ConnectionException"
-                except ConnectionException:
-                    pass
 
     def test_close(self):
         self._setup_mocked_http()
@@ -298,19 +295,13 @@ class TestZyxelVMGDriver:
 
     def test_load_replace_candidate_raises(self):
         self._setup_mocked_http()
-        try:
+        with pytest.raises(NotImplementedError):
             self.driver.load_replace_candidate()
-            assert False, "Expected NotImplementedError"
-        except NotImplementedError:
-            pass
 
     def test_load_merge_candidate_raises(self):
         self._setup_mocked_http()
-        try:
+        with pytest.raises(NotImplementedError):
             self.driver.load_merge_candidate()
-            assert False, "Expected NotImplementedError"
-        except NotImplementedError:
-            pass
 
     def test_ping_not_implemented(self):
         self._setup_mocked_http()
@@ -325,11 +316,8 @@ class TestZyxelVMGDriver:
         from napalm.base.exceptions import ConnectionClosedException
 
         self.driver._session = None
-        try:
+        with pytest.raises(ConnectionClosedException):
             self.driver._dal_query("PINGTEST", {})
-            assert False, "Expected ConnectionClosedException"
-        except ConnectionClosedException:
-            pass
 
     def test_parse_port_forwards_dal(self):
         self._setup_mocked_http()