MFC r354446: rc.shutdown: print a newline before watchdog timeout message

Previously the watchdog timeout message was appended to the last entry
in the "Waiting for PIDS" list, resulting in a message like

Waiting for PIDS: 31299 31296 90201 9020090 second watchdog timeout
expired. Shutdown terminated.

Print a newline to separate the watchdog timeout message.

Also MFC 355476: rc.shutdown: kill shutdown process after logging message

Move the kill -KILL $$ back to the pre-r354446 location at the end of
the shutdown timeout handler.

PR: 241072
Sponsored by: The FreeBSD Foundation