PlatformNotSupportedException - when setting MaxConnectionsPerServer

From this review: http://review.couchbase.org/#/c/72835/ Matt Ingenthron asks: _{"... is this normal on .NET Core? It seems odd to me that something like HttpClient can have a different approach even down to a per-Linux distro basis."}

This ticket is to spend some time looking into this and come up with a generally acceptable approach.