fix for thetao and so variables in BCC models

[koldunovn]

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Closes #748

[nielsdrost]

@koldunovn Could this be causing the problem with the BCC dataset in ESMValGroup/ESMValTool#1391?

Anything that still needs to be done on this, or is it waiting for a review?

[koldunovn]

@nielsdrost This fix is only for two ocean variables that I can personally check (so and thetao). Looks like the problems @ValerioLembo having are for atmospheric variables (sorry, did not go through all conversation, it's super long now :))).

I would consider the PR ready, but you might want to expand it with atmospheric variables. On the other hand I would do one thing at a time, makes it easier to handle :)

[valeriupredoi]

@koldunovn cheers mate, I think this one's good to go - but a test would be nice to have for the new functionality please 🍺

[valeriupredoi]

ping @koldunovn for a testy-test please 🍺

[schlunma]

Will have a look at this after #1092 is merged. It can probably be fixed with

Thetato = OceanFixGrid

[zklaus]

I believe this has meanwhile been addressed in #1090 and #1092.