[pktverify] verify offline test info (#5525)

This commit allows running packet verification on a test info (.json)
directly without running the test procedure, which can be helpful for
developing and debugging packet verification code.

tests/scripts/thread-cert/thread_cert.py

@@ -348,6 +348,7 @@ class TestCase(NcpSupportMixin, unittest.TestCase):
             return
 
         test_info = self._test_info = {
+            'script': os.path.abspath(sys.argv[0]),
             'testcase': self.test_name,
             'start_time': time.ctime(self._start_time),
             'pcap': '',