[reboot] Add newline in the expected output in unit test.

Signed-off-by: Yong Zhao <[email protected]>

tests/reboot_cause_test.py

@@ -31,7 +31,7 @@ def setup_class(cls):
 
     # Test 'show reboot-cause' without previous-reboot-cause.json 
     def test_reboot_cause_no_history_file(self):
-        expected_output = "Unknown"
+        expected_output = "Unknown\n"
         runner = CliRunner()
         result = runner.invoke(show.cli.commands["reboot-cause"], [])
         assert result.output == expected_output