Test: Add `test_server` module

Currently only API-compatibility between 'our' server and the upstream
Swift one is validated.
Fix API compatibility with Swift 2.2.0

See: 77be658497e1c31e9454ef814a7631a5b9420386
Update version bounds to support Swift 1.13.1
Add Swift 1.13.1 API compatibility
Merge pull request #15 from scality/support-1.13

Support 1.13