rcutorture: Make kvm-recheck.sh export TORTURE_SUITE

As it should, the kvm-recheck.sh script sets the TORTURE_SUITE bash
variable based on the type of rcutorture test being run.  However,
it does not export it.  Which is OK, at least until you try running
kvm-again.sh on either a rcuscale or a refscale test, at which point you
get false-positive "no success message, N successful version messages"
errors.  This commit therefore causes the kvm-recheck.sh script to export
TORTURE_SUITE, suppressing these false positives.

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