[WIP] http4s - migrate from Blaze to Ember

[ivan-klass]

Ember seems to be more modern and especially better supported in terms of cross-platform builds

[adamw]

Oh nice, I was worried you abandoned the PR ;)

[ivan-klass]

Will wait for #4267 first

[ivan-klass]

@adamw when you have a chance, could you please take a look on #4267 so I can rebase this PR on top of that?

[adamw]

@ivan-klass sure thing, done :)

[ivan-klass]

To whom it may concern: ember builder doesn't have an option for a specific execution context, so test request handling is not in the global one as it was before. It seems like race conditions are observed when dealing with some web-socket tests.

[adamw]

@ivan-klass sorry for the delay - the global EC was used before only because it was the easiest one to obtain ;). I don't think there's anything in the tests that would rely on the global one being used: each server should be independent anyway, regardless on the thread pool on which tasks/futures are scheduled. So I would look for causes of the exceptions elsewhere, unfortunately.

[ivan-klass]

Then there might be a bug in http4-ember then... I'll try to dig in and reproduce when I have time