Fix all flake8 errors in satpy package code

[djhoese]

I ran flake8 satpy from the root of the repository and got a lot of errors. I walked through these errors and fixed all but one of them. All of them were style changes except one.

The one I didn't fix is the li_l2 reader which hasn't been migrated to xarray/dask yet. Instead of removing the failing import I added the reader to the ignored paths in setup.cfg.

The only non-style change was in the mitiff writer (@TAlonglong) where there were bare except statements (except:). I changed these to except (KeyError, ValueError, RuntimeError): to make flake8 happy and hopefully not change any functionality of the writer. @TAlonglong please verify that these exceptions are what you expected. Catching all errors by doing except: or except Exception: is considered bad practice.

Lastly, some of these changes were just personal preference changes, but still changes that I think go along with the conventions that @pytroll/core have talked about in the past on slack. Some were also to reduce number of broken lines now that we've agreed on 120 max line length.

• Closes Flake8-ify all of satpy #467
• Passes git diff origin/master -- "*py" | flake8 --diff

[coveralls]

Coverage increased (+0.06%) to 74.621% when pulling fcd71f6 on djhoese:style-fixes into c2a2a44 on pytroll:master.

[djhoese]

Wow I really thought I would have gotten more than 0.06% coverage increase.

[codecov]

Codecov Report

Merging #515 into master will increase coverage by 0.05%.
The diff coverage is 68.13%.

@@            Coverage Diff             @@
##           master     #515      +/-   ##
==========================================
+ Coverage   74.56%   74.62%   +0.05%     
==========================================
  Files         136      136              
  Lines       18400    18342      -58     
==========================================
- Hits        13720    13687      -33     
+ Misses       4680     4655      -25

Impacted Files	Coverage Δ
satpy/readers/ghrsst_osisaf.py	23.88% <ø> (ø)	⬆️
satpy/tests/reader_tests/test_hdf4_utils.py	92.06% <ø> (ø)	⬆️
satpy/readers/acspo.py	85.71% <ø> (ø)	⬆️
satpy/composites/crefl_utils.py	83.33% <ø> (-0.3%)	⬇️
satpy/tests/reader_tests/test_msg_base.py	95% <ø> (+10.38%)	⬆️
satpy/tests/reader_tests/test_utils.py	71.87% <ø> (-0.29%)	⬇️
satpy/tests/reader_tests/test_netcdf_utils.py	93.24% <ø> (ø)	⬆️
satpy/tests/test_file_handlers.py	97.1% <ø> (-0.05%)	⬇️
satpy/tests/writer_tests/test_mitiff.py	95.55% <ø> (-0.28%)	⬇️
satpy/tests/reader_tests/test_hdf5_utils.py	92.64% <ø> (ø)	⬆️
... and 35 more

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