* Initial IPv6 connection support

TL;DR: We previously did IP:Port parsing based on splitting at the semicolon...that's pretty hostile for IPv6 and breaks everything. This adopts better parsing from Microsoft.AspNetCore since it doesn't exist in the BCL. The BCL/API conversation is started here: https://github.com/dotnet/corefx/issues/23463

A quick way to test this across all tests is via TestConfig, for example:
{
  "MasterServer": "[::1]",
  "SlaveServer": "[::1]",
  "SecureServer": "[::1]"
}

Note: there's still an Unspecified == AddressFamily.InterNetwork in SocketManager which may be affecting DNS endpoints that are v6...need to look at that next. This change allows actually connecting to an IPv6 endpoint via IP though, that's step 1.

* Move BasicStringGetPerf to non-parallel

* Fix IPv4 assumptions

The socket world has changed - unspecified and dual mode sockets now handle IPv6 correctly. We can just straight up remove the assumption of IPv4 anywhere in code now.