open_mfdataset fails when datacubes have different chunking

I am not sure what we can do about it, but if we try to open two datasets that have a slightly different chunking via open_mfdataset this fails with an Argument Error: Chunk sizes do not form a grid. 

It would be nice, if we could try to circumvent this error by setting the chunks of the cubes all to the same chunking structure. 

