torture: s/STOP/STOP.1/ to avoid scenario collision

This commit changes the "STOP" file that is used to cleanly halt a running
rcutorture run to "STOP.1" because no scenario directory will ever end
with ".1".  If there really was a scenario named "STOP", its directories
would instead be named "STOP", "STOP.2", "STOP.3", and so on.  While in
the area, the commit also changes the kernel-run-time checks for this
file to look directly in the directory above $resdir, thus avoiding the
need to pass the TORTURE_STOPFILE environment variable to remote systems.

While in the area, move the STOP.1 file to the top-level directory
covering all of the scenarios.

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