Temporarily remove longitude/latitude 2D xarray coordinates

[djhoese]

This was discovered while testing #836. Xarray currently has a bug (of sorts) where any dask array coordinates are computed whenever two xarray DataArrays are combined. See the related xarray issue. Until this is resolved better on the xarray/dask side we need to stop adding these coordinates.

As is, this requires a lot of computation to load/compute these geolocation arrays.

• Tests added and test suite added to parent suite
• Tests passed
• Passes flake8 satpy

[djhoese]

This also includes small changes to the Filler compositor to check areas before trying to operate on the data. And a change to yaml_reader.py so that the name of a SwathDefinition is only set once.

[mraspaud]

LGTM. I thought I had questions on this, but on closer inspection it looks clear to me.

[mraspaud]

One question: am I understanding correctly that the coords are still there in case of a swath ?

[djhoese]

@mraspaud Which coords? In the case of a SwathDefinition based DataArray there will be no coordinates with this PR. Without this PR and pyproj 2.0+ installed you would get longitude and latitude, without this PR and pyproj <2.0 you would not get any coordinates.

[mraspaud]

ok, good

[coveralls]

Coverage decreased (-0.0005%) to 83.983% when pulling 714fb21 on djhoese:bugfix-lonlat-coords into 44239a0 on pytroll:master.

[djhoese]

As noted on slack, the OSX tests were failing because conda was hanging for some reason. For now I'm going to assume that this is a known issue with conda or ci-helpers and will continue focusing on making a patch release in the next day or so.