Log the required inputs, instead of raising exceptions

Change-Id: If154aeebf277b3374aaff9c6b5d1d9522ea6c13c
Closes-Bug: #1653992

toscaparser/topology_template.py

@@ -76,10 +76,8 @@ class TopologyTemplate(object):
             if (self.parsed_params and input.name not in self.parsed_params
                 or self.parsed_params is None) and input.required \
                     and input.default is None:
-                exception.ExceptionCollector.appendException(
-                    exception.MissingRequiredParameterError(
-                        what='Template',
-                        input_name=input.name))
+                log.warning(_('The required parameter %s '
+                              'is not provided') % input.name)
 
             inputs.append(input)
         return inputs