torture: Add "scenarios" option to kvm.sh --dryrun parameter

This commit adds "--dryrun scenarios" to kvm.sh, which prints something
like this:

1.  TREE03
2.  TREE07
3.  SRCU-P SRCU-N
4.  TREE01 TRACE01
5.  TREE02 TRACE02
6.  TREE04 RUDE01 TASKS01
7.  TREE05 TASKS03 SRCU-T SRCU-U
8.  TASKS02 TINY01 TINY02 TREE09

This format is more convenient for scripts that run batches of scenarios.

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