Provide a method to wait in the initramfs

Created by: ollieparanoid

From reading the chatlog, that would have been useful for ayr3s, because the booting process got stuck after killing the usb-shell telnet daemon and before starting sshd.

Idea: In the usb-shell hook, check for a new kernel parameter, and if it is present, simply wait forever (or drop to a shell?).

What do you think?