rcutorture: Make kvm-find-errors.sh find close calls

Although warnings about close calls are printed by kvm-recheck.sh,
kvm-find-errors.sh currently ignores them.  This could easily result
in someone failing to investigate close calls, so this commit makes
them visible to kvm-find-errors.sh.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>