send binding_options to service_gateway

Required for vCHS Services -- binding_options allows sharing a service_instance with reduced privileges (for example, a 'read-only' binding-option for a relational DB would allow SELECT queries but not INSERT, UPDATE or DELETE).

Binding options are already in CCDB and supported by service gateways.  So this is a pretty simple change: just send them, instead of sending nil.

(FYI -- a similar PR for plan_options in a provision request is on the way...)