torture: Print proper vmlinux path for kvm-again.sh runs

The kvm-again.sh script does not copy over the vmlinux files due to
their large size.  This means that a gdb run must use the vmlinux file
from the original "res" directory.  This commit therefore finds that
directory and prints it out so that the user can copy and pasted the
gdb command just as for the initial run.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>