rcutorture: Eliminate configdir argument from kvm-recheck.sh script

Don't grab the configuration fragment from the configs directory because
it might well have been changed since the test was run.  Instead, use
the ConfigFragment file that was placed in the results directory.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Greg KH <gregkh@linuxfoundation.org>