Hande exif orientation with pillow backend in imread

[daavoo]

The default behavior of imread with the pillow backend ignores the exif orientation tag, resulting in inconsistencies with the default backend (cv2) which properly handles it. This P.R. adds a regression test and updates _pillow2array to match the behavior of the cv2 backend.

[codecov]

Codecov Report

Merging #805 (6bfd911) into master (9e601ca) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #805      +/-   ##
==========================================
+ Coverage   61.94%   61.97%   +0.02%     
==========================================
  Files         144      144              
  Lines        8467     8468       +1     
  Branches     1520     1520              
==========================================
+ Hits         5245     5248       +3     
+ Misses       2954     2953       -1     
+ Partials      268      267       -1     

Flag	Coverage Δ
unittests	61.97% <100.00%> (+0.02%)	⬆️

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

Impacted Files	Coverage Δ
mmcv/image/io.py	90.75% <100.00%> (+1.77%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9e601ca...6bfd911. Read the comment docs.

[hellock]

Thanks for the nice fix!