change service_id parameter

old parameter "service-id" has now changed to "service_id"

>keystone help endpoint-create
>usage: keystone endpoint-create [--region <endpoint-region>]
                                [--service_id <service-id>]
                                [--publicurl <public-url>]
                                [--adminurl <admin-url>]
                                [--internalurl <internal-url>]