tools/memory-model: Make judgelitmus.sh ransack .litmus.out files

The judgelitmus.sh script currently relies solely on the "Result:"
comment in the .litmus file.  This is problematic when using the --hw
argument, because it is necessary to check the hardware model against
LKMM even in the absence of "Result:" comments.

This commit therefore modifies judgelitmus.sh to check the observation
in a .litmus.out file, in case one was generated by a previous LKMM run.

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