Support npipe the same way we support Unix sockets
Support npipe the same way we support Unix sockets

The same function used to support Unix sockets automatically supports
Named Pipes on Windows.

This makes the default configuration option for the daemon address work
correctly on Windows.

Signed-off-by: Paul "TBBle" Hampson <220d126b3d70d9d7b0fda508e4cb236265bccc41@Pobox.com>

tonistiigi/buildkit_poc,tonistiigi/buildkit_poc