Add ConvertHelper.ConvertAll, which uses Array.ConvertAll() for Non-dnx, and add implementation for dnx.

Replace usage of SpinWait struct with simple increment operation.  SpinWait.SpinOnce() takes too much time than the original Thread.SpinWait(5).

Update moq.netcore to 4.4.0.  The old version didn't specify its dependencies for the 'dotnet' group.

Trace IOException for stream.Read(). Otherwise the IO exception would be wrapped in an AggregateException, which would not be caught by the try-catch around BeginRead() method call.

Also unwrap AggregateException in EndRead() and re-throw its inner exception.

Use Volatile wrapper.

Merge branch 'UpdateNUnitTo3' of https://github.com/RogerBestMsft/StackExchange.Redis into netcore-test