Adding run1dir and run2dir to lettuce.world
Adding a terrain.py file

This is a file for adding pre/post hooks and world.absorb/spew
functions/objects.

I have added a @after.each_scenario hook that prints out world.message
if one has been created within a scenario.
Updating LI features so that Halfar test works
Switching lettuce.config to lettuce.CORE

Now given_a_setup_test_environment() in mpas_tasks.py has logic to
figure out which core is being run and then open the core-specific
config file.
I have deleted lettuce.config and added lettuce.ocean lettuce.landice.
Adding post-scenario hook to return to basedir

This is so if a scenario has an unexpected error that leaves PWD in some
strange place, the next scenario still has a chance to run correctly.