Remove Task.Delay() calls and use a TaskCompletionSource instead.

Waiting for a task delay is slower than it needs to be and in some cases
caused errors in the tests (a race condition was introduced).
If a TaskCompletionSource is used instead, then the test will resume
once the necesary asynchronous steps have completed.
Additonally added use of TestOutputHelper and some logger
implementations that allow the log output from the code under test to be
output in the test output (viewable with verbose output) e.g.:

 dotnet test --framework NET471 --logger "console;verbosity=detailed"