Reenable multi-process transport tests

[pietern]

These were disabled in #230 because they all fail when running consecutively.

When run independently, they appear to pass...

[facebook-github-bot]

Hi @pietern!

Thank you for your pull request. We require contributors to sign our Contributor License Agreement, and yours needs attention.

You currently have a record in our system, but we do not have a signature on file.

In order for us to review and merge your code, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

If you have received this in error or have any questions, please contact us at [email protected]. Thanks!