Support S3 V2 signing

[fuku2014]

Some S3 clones only support v2 signing and not the v4 signing.

It should be support s3 sign like aws-cli.

[default]
s3 =
    signature_version = s3

[tboerger]

First you should fork the plugin, add the changes and try it with your fork. When it's working fine you can create a pull request and we will see what else needs to be changed