torture: Allow #CHECK# in --kconfig argument to kvm.sh

Testing building of a given RCU Tasks flavor with the other two
flavors disabled requires checking that the other two flavors are in
fact disabled.  This commit therefore modifies the scripting to permit
things like "#CHECK#CONFIG_TASKS_TRACE_RCU=n" to be passed into the
kvm.sh script's --kconfig parameter.

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