Strip the leading /dev/ from the console path

The kernel cmdline doesn't like /dev/${console}, use ${console}
instead.

Change-Id: I834cb74ac27c415537eb480694905c349f3164d5
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=966302
Signed-off-by: Ryan Barry <rbarry@redhat.com>