Handling of missing URL parameter on REST carrier plugins incorrect

The URL parameter must always be provided on the REST client carrier plugin

The URL parameter must always be provided on the REST requestor consumer

The URL parameter is not required on the REST requestor producer

This patch fixes the implementation to always checks the URL for existence on the REST Client plugin. The current checks on the REST Requestor are correct for the REST requestor plugin consumer and producer classes, so the checks are not required in the REST Requestor parameters.