follow up on duplex operation for HTTP/2 (dotnet/corefx#38226)

follow up on duplex operation for HTTP/2 (dotnet/corefx#38226)

* follow up on duplex operation

* updates

* add test for cancelation

* log responseHeadersTask if bodyTask fails first

* improve cancelation

* feedback from review

* update SendAsync_ConcurentSendReceive_Fail test

* feedback from review

* update SendSettingsAckAsync

* more HTTP/2 cancelation tests

* update test to accept any derivative from OperationCanceledException

* feedback from review

* roll-back changes in AcceptConnectionAsync

Commit migrated from https://github.com/dotnet/corefx/commit/cad5159981f518f455be3528d0ee8eca2e00742a