Sentinel: sentinelRefreshInstanceInfo() minor refactoring.

Test sentinel.tilt condition on top and return if it is true.
This allows to remove the check for the tilt condition in the remaining
code paths of the function.
Unify stats reset for CONFIG RESETSTAT / initServer().

Now CONFIG RESETSTAT makes sure to reset all the fields, and in the
future it will be simpler to avoid missing new fields.