Bug mitiff writer when only one channel is to be written with calibration information

[TAlonglong]

There is a bug in the mitiff writer when saving only one channel with calibration information. The writer assumed datasets to be a list at one point and used the 'bands' dimension when it was not there.

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

[codecov]

Codecov Report

Merging #792 into master will increase coverage by 0.65%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #792      +/-   ##
==========================================
+ Coverage   82.27%   82.93%   +0.65%     
==========================================
  Files         159      163       +4     
  Lines       22996    23579     +583     
==========================================
+ Hits        18921    19555     +634     
+ Misses       4075     4024      -51

Impacted Files	Coverage Δ
satpy/tests/writer_tests/test_mitiff.py	97.96% <100%> (+1.38%)	⬆️
satpy/writers/mitiff.py	91.68% <100%> (+11.8%)	⬆️
satpy/readers/seviri_l1b_nc.py	15.53% <0%> (-2.29%)	⬇️
satpy/writers/utils.py	100% <0%> (ø)
satpy/tests/reader_tests/test_vaisala_gld360.py	96% <0%> (ø)
satpy/tests/writer_tests/test_utils.py	93.33% <0%> (ø)
satpy/readers/vaisala_gld360.py	90% <0%> (ø)
satpy/tests/reader_tests/__init__.py	98% <0%> (+0.04%)	⬆️
satpy/scene.py	90.08% <0%> (+0.17%)	⬆️
satpy/tests/writer_tests/test_cf.py	98.91% <0%> (+0.23%)	⬆️
... and 7 more

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[coveralls]

Coverage increased (+0.7%) to 82.93% when pulling 347ed6c on TAlonglong:bug-mitiff-writer-only-one-channel into cd65262 on pytroll:master.

[mraspaud]

@TAlonglong is this ready to be merged ?

[TAlonglong]

It should be, but I looked quick at the test coverage and it looks a bit strange. So I need to check things over again. Maybe today, if not I will take a few days of, then next week.

[mraspaud]

No problem, take your time. Just ping me when you want this merged.

[TAlonglong]

Think I'm done now. Can you have a look @mraspaud when you can spare some time?

[mraspaud]

LGTM