Change NodeUnavailableException Base Class And Other Exception Issues

.Net Core does not include remoting or the System.Runtime.Remoting namespace. Currently, NodeUnavailableException is inherited from System.Runtime.Remoting.ServerException. This base class should be changed to a more consistent base class, such as Exception.

ApplicationException is no longer available, either. Apparently the .Net approach has been to move away from it, and recommend inheriting your exceptions directly from Exception. There is one location in code throwing ApplicationException directly, which should be changed to Exception or a new class created. This is edge case code, so it should be safe to change without breaking compatibility.