python: Fix yaml.load warnings

Since pyyaml 5.1 yaml.load without specifing loader is deprecated
Details: https://msg.pyyaml.org/load

To keep code compatible with older versions of pyyaml
and keep best perfomance CLoader with fallback to Loader is used.

tools/tiny-test-fw/CIAssignUnitTest.py

@@ -9,6 +9,11 @@ import argparse
 
 import yaml
 
+try:
+    from yaml import CLoader as Loader
+except ImportError:
+    from yaml import Loader as Loader
+
 try:
     from Utility import CIAssignTest
 except ImportError:
@@ -110,7 +115,7 @@ class UnitTestAssignTest(CIAssignTest.AssignTest):
 
         try:
             with open(test_case_path, "r") as f:
-                raw_data = yaml.load(f)
+                raw_data = yaml.load(f, Loader=Loader)
             test_cases = raw_data["test cases"]
         except IOError:
             print("Test case path is invalid. Should only happen when use @bot to skip unit test.")