Fix error message when zfs module is not loaded

This patch corrects a small issue where the wrong error message
was being displayed when the zfs kernel module was not loaded.
This also avoids waiting for the (by default) 10s timeout to see
if the /dev/zfs device appears.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #8187