'Extract a dictionary of user input parameters for the stack.
In the AWS API parameters, each user parameter appears as two key-value
pairs with keys of the form below::
Parameters.member.1.ParameterKey
Parameters.member.1.ParameterValue'

@staticmethod
def _extract_user_params(params):

    return api_utils.extract_param_pairs(params, prefix='Parameters', keyname='ParameterKey', valuename='ParameterValue')
