[v0.16.x] Migrate to new s3 URL method

[tjamet]

Path based access has been deprecated and now returns a redirect error to bucketname.s3.amazonaws.com
as explained in this post:
https://aws.amazon.com/blogs/aws/amazon-s3-path-deprecation-plan-the-rest-of-the-story/

This makes cloudformation to fail as it refers to the now redirected s3
bucket path, and raises the message:
S3 error: The bucket you are attempting to access must be addressed using the specified endpoint. Please send all future requests to this endpoint. For more information check http://docs.aws.amazon.com/AmazonS3/la

There is no strong documentation about what are the updates in China and
Gov regions, consider it follows the same logic.

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[codecov-commenter]

Codecov Report

Merging #1873 into v0.16.x will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           v0.16.x    #1873      +/-   ##
===========================================
- Coverage    24.41%   24.40%   -0.01%     
===========================================
  Files           98       98              
  Lines         5116     5117       +1     
===========================================
  Hits          1249     1249              
- Misses        3727     3728       +1     
  Partials       140      140              

Impacted Files	Coverage Δ
pkg/api/assets.go	0.00% <0.00%> (ø)
pkg/api/region.go	0.00% <0.00%> (ø)

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[Fsero]

/assign @dominicgunn

[Fsero]

@tjamet could you please also patch 0.15.x and 0.14.x?

[tjamet]

@Fsero yes sure, did this first one for the approach to focus discussion and planned to do so when convergence on the solution

[dominicgunn]

Thanks for doing this @tjamet! The approach here seems good.

/lgtm

[dominicgunn]

Thanks for doing this @tjamet! The approach here seems good.

/lgtm