Fix platform_name and sensor not being added by avhrr eps l1b reader

[TAlonglong]

Need to add platform_name and sensor in attrs for avhrr eps l1b reader.

[coveralls]

Coverage decreased (-0.009%) to 71.702% when pulling 1bdb6da on TAlonglong:fix-eps-avhrr-attrs into 633ade3 on pytroll:master.

[codecov]

Codecov Report

Merging #412 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master    #412      +/-   ##
=========================================
- Coverage   71.71%   71.7%   -0.01%     
=========================================
  Files         126     126              
  Lines       16614   16616       +2     
=========================================
  Hits        11914   11914              
- Misses       4700    4702       +2

Impacted Files	Coverage Δ
satpy/readers/eps_l1b.py	18.13% <0%> (-0.18%)	⬇️

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