initscript: drop the poweroff section

When running boot2container on real machines with serial consoles, the "It's now safe to turn off your computer" message is the trigger to stop execution and shut down the connection. This means we never get the "section_end" message over the serial console and the section will swallow everything else that comes after.

This patch removes this issue by closing the section before the message gets sent... at the expense of a couple of extra lines in the logs... Sorry!