Bug#983357: Netinst crashes xen domU when loading kernel

[Phillip Susi <phill@thesusis.net>]

The discussion upstream does not seem to be converging on a proper fix
in the kernel, so I'm going to clone this bug and suggest that
debian-installer patch the start-udev script to ignore the failure of
the udevadm trigger command.

To summarize: init ends up calling start-udev which calls udevadm
trigger to cold plug all devices.  Both scripts are set -e.  The Xen
Virtual Keyboard driver and at least one other driver have always failed
to trigger due to having absurdly long modalias, but the error used to
be ignored.  The kernel now returns the error to udevadm, so it exits
with an error, so start-udev exits with an error, so init exits with an
error, causing the kernel to panic.