The tests do not build at API_LEVEL=8

[travisdowns]

When using --api-level=8 (on less than the current level 9), ninja seastar is OK, but trying to build the tests failed (largely around the input stream adjustments to use temporary_buffer over packet).

I'm not sure if this is considered a bug and if patches would be accepted to fix this, or if this is by design.

Currently we are on API level < 9 so we have an interest here as we run seastar tests in CI on our fork.

[travisdowns]

Well this turned out to be easy to fix so I'll submit a patch.