Fix get_param_heat_template.py for hot templates

hot templates are not just key:value dict,
there are 'default' keys with the required values.

Change-Id: If0f0cc8d6de9b7d5fc7f048e9f1d608ff76b46ed
diff --git a/tcp_tests/utils/get_param_heat_template.py b/tcp_tests/utils/get_param_heat_template.py
index 9b8b236..09a2450 100755
--- a/tcp_tests/utils/get_param_heat_template.py
+++ b/tcp_tests/utils/get_param_heat_template.py
@@ -48,7 +48,8 @@
 parameter_name = sys.argv[1]
 parameter_value = env['parameter_defaults'].get(parameter_name)
 if parameter_value is None:
-    parameter_value = template['parameters'].get(parameter_name)
+    parameter_template = template['parameters'].get(parameter_name, {})
+    parameter_value = parameter_template.get('default')
     if parameter_value is None:
         raise Exception("Parameter '{0}' not found in env file '{1}' "
                         "and temlate file '{2}'"