Fix undefined method 'version_id' during multipart upload

[menno]

I got the following error when a large file got automatically uploaded via multipart-upload to S3:

NoMethodError: undefined method `version_id' for #<Hash:0x00000006b94b40>
    from //shared/bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/core/data.rb:101:in `method_missing'
    from //bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/core/data.rb:121:in `method_missing'
    from //bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/core/response.rb:193:in `method_missing'
    from //bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/s3/multipart_upload.rb:245:in `complete'
    from //bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/s3/multipart_upload.rb:267:in `close'
    from //bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/s3/s3_object.rb:707:in `multipart_upload'
    from //bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/s3/s3_object.rb:1619:in `write_with_multipart'
    from //bundle/ruby/1.9.1/gems/aws-sdk-1.8.1.1/lib/aws/s3/s3_object.rb:598:in `write'

Comparing how a single-part upload was handled I made a change in how the version_id is handled from the response. This patch solved the issue for me.

The related spec does not fail without the patch, this could be due the response being a stub. But I'm not sure of this. Also I could not find any specs for a multipart-upload to a versioned bucket.

[trevorrowe]

Thanks for the PR. I'll take a look at the cause to this and check whats up with the test.

[trevorrowe]

I merged this locally and pushed your commit (542f075). I was able to isolate the issue with the specs not failing (https://github.com/aws/aws-sdk-ruby/commit/793aa0d4f38e866db0d0bbe952bce791f46615ad#spec/aws/s3/multipart_upload_spec.rb#diff-1). Thanks for the fix!