Log on set delay

[pkolbeck]

Log_on_set immediately logs the endpoint upon setting.
Some instruments take time to change the setting to the new value. Being able to delay the log to be some amount of time after the set can be useful, possibly via a Log_on_set_delay option for endpoint configuration.

[wcpettus]

two quick thoughts:

• most devices I've dealt with the delay can be quite modest (1 sec or even much less), but curious what your experience is expecting for the worst device
• probably use service.schedule to not lock the return?