Related https://github.com/dotnet/corefx/issues/9350

In PowerShell repo we port TestConnection cmdlet and catch some problems in the ping API.

The problems documented in the cmdlet tests - see comments and if (!isWindows) blocks.

Below short list:

1. Dontfragment doesn't work on Unixes
   This definitely should work on Linux and on MacOs too
2. PingReply.Buffer is empty on Unix. Expected - a buffer we send.
3. Ping unreachable host returns ErrorCode 6 (Handle is invalid) on Unix. Expected (as on Windows) - 11001 (Host not found).
4. API always returns Options based on default PingOptions() constructor (Ttl=128, DontFragment = false).
   PingReply.Options.DontFragment:

• on Windows always returns false. Expected - real value from ping request.
• on Unix always returns null. Expected - real value from ping request (or false if not implemented).

PingReply.Options.Ttl - always 128. Expected - real value from ping request.
PingReply.Options.Status - always Success (if we expect 'TtlExpired'). Expected - real status.

5. PingReply doesn't return ScopeId in IPAddress