Introduce OpenRemoteKey function that opens some
root registry keys on remote computer.

Also add PERFORMANCE_DATA key, since it is one of
root keys accessible via OpenRemoteKey.

Change-Id: I738fdfee52a34acd4dc09ddb91fcf0e4c707bd83
Reviewed-on: https://go-review.googlesource.com/33814Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>