Porting some tests from 2.0, changed MemoryPoolWriter binary write funct...

...ion to WriteRawBytes
This test is out of date. It looks like it's out of the master branch instead of [dev](https://github.com/SignalR/SignalR/blob/dev/tests/Microsoft.AspNet.SignalR.Tests/TaskAsyncHelperFacts.cs).

I tried running the newer tests in this project and it builds, but the `PreserveCultureAwaiterPreservesCulture` test fails. That's something that I'll have to look into tomorrow.

I would update this to the newer version of the test anyway and maybe skip the test that is failing for now. It would also be nice if you could double check to see if you are missing anything else from dev.