rcutorture: Print script and arguments to standard output

Although the script name and arguments are logged in the results directory,
it is more convenient to see it in the output.  This commit therefore
adds the output of this information.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>