Convert integration tests to run against both Akka HTTP and Netty

Not all tests are currently working with Akka HTTP. Failing tests are marked with `pendingUntilAkkaHttpFixed` or `skipUntilAkkaHttpFixed` so that they don't cause test failures.

After this change, the integration tests show:
```
[info] Passed: Total 325, Failed 0, Errors 0, Passed 324, Skipped 1, Pending 41
```