added -s3-force-path-style flag

[nebehr]

Added a flag to force path-style addressing during file upload from Selenoid to S3 (i.e. http://s3.amazonaws.com/BUCKET/KEY instead of http://BUCKET.s3.amazonaws.com/KEY), disabled by default.

[codecov]

Codecov Report

Merging #614 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #614      +/-   ##
==========================================
+ Coverage   78.23%   78.26%   +0.03%     
==========================================
  Files          12       12              
  Lines        1369     1371       +2     
==========================================
+ Hits         1071     1073       +2     
  Misses        228      228              
  Partials       70       70

Flag	Coverage Δ
#unittests	78.26% <100%> (+0.03%)	⬆️

Impacted Files	Coverage Δ
upload/s3.go	84.7% <100%> (+0.36%)	⬆️

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[vania-pooh]

@nebehr thank you for contribution!