Update tests to be more flexible to CRS and enhancement changes

[djhoese]

This is an update needed for pytroll/pyresample#415 so that satpy tests still pass with those pyresample changes. One lesson learned is that +init=EPSG:XXXX does not respect the axis order of the EPSG definition. Using EPSG:XXXX does.

This PR also includes refactoring of the enhancements tests because they were causing failures when combined with my trollimage PR here: pytroll/trollimage#99

• Tests added

[codecov]

Codecov Report

Merging #2002 (a8067a0) into main (3e94d59) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2002      +/-   ##
==========================================
- Coverage   93.54%   93.54%   -0.01%     
==========================================
  Files         279      279              
  Lines       41322    41317       -5     
==========================================
- Hits        38654    38649       -5     
  Misses       2668     2668              

Flag	Coverage Δ
behaviourtests	4.78% <0.00%> (+<0.01%)	⬆️
unittests	94.07% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/tests/enhancement_tests/test_enhancements.py	100.00% <100.00%> (ø)
satpy/tests/enhancement_tests/test_viirs.py	100.00% <100.00%> (ø)
satpy/tests/reader_tests/test_generic_image.py	98.90% <100.00%> (ø)

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[pnuu]

LGTM

[coveralls]

Coverage decreased (-0.0007%) to 94.004% when pulling a8067a0 on djhoese:refactor-crs-flexibility into 3e94d59 on pytroll:main.

[mraspaud]

LGTM