Address CA not working with non-uniform blocksizes

[lisa-bengtsson]

Description

Currently the cellular automata scheme only works with uniform blocksizes limiting the layout combination used.

Solution

Update the code to work also on non-uniform blocksizes by making a small change stochastic_physics_driver.F90 to allow the cellular automata to work on non-uniform blocksizes. Previously the code aborted if not all blocks in the domain had the same size, however, the code works the way it's been formulated, so I simply removed the call to mpp_error in case on non-uniform blocksizes.