SCO tests

[jdha]

Ideas

• with SF12 and SH94 any depth shallower than hc should be uniform sigma i.e. all e3t in a 1D profile should be identical
• using the sea mount case check that the e3t at different depths scale proportionally to H (again this is for SF12 and SH94; not too sure how it would work with MEs)
• with @jdha hybrid SZ we could use the ZCO tests in the open ocean and the two cases above
• MEs? I'll let @oceandie suggest a few things
• rmax/evelope bathy check: with a bathy that doesn't exceed the rmax all sigma levels should be present. with a bathy that does exceed rmax bottom_level will be non-uniform

[oceandie]

I think all the tests @jdha proposed should work also with MEs, let's try it ...