Simplify control_event_bootstrap() by making it return void again.  It
is currently a fairly complicated function, and it's made more
complicated by returning an int to signal whether it logged at NOTICE
or INFO.

The callers conditionally log messages at level NOTICE based on this
return value.  Change the callers to unconditionally log their verbose
human-readable messages at level INFO to keep NOTICE logs less
cluttered.

This partially reverts the changes of #14950.