helper: Fix confusing verbose message.

Previously the messages would say:

checking modpath /lib/modules/3.9.9-302.fc19.armv7hl.lpae is a directory
picked vmlinuz-3.9.9-302.fc19.armv7hl.lpae because modpath /lib/modules/3.9.9-302.fc19.armv7hl.lpae exists

However this appears to indicate that the kernel was "picked".  In
fact, it just passed the modpath test, and it's not necessarily the
kernel that we're going to pick.
helper: On arm, don't choose a .lpae or .tegra kernel.

The vexpress-aX emulation we are using in qemu doesn't support these
kernels.
helper: init: Print a message while waiting for root to appear.

It will now print:

supermin: waiting another 1024000000 ns for /sys/block/vda/dev to appear
supermin: waiting another 2048000000 ns for /sys/block/vda/dev to appear
supermin: waiting another 4096000000 ns for /sys/block/vda/dev to appear
[etc]

if there is a long wait for the root device to be enumerated.