add mac back to match_nodes_on so it can be searched

Windows installer scripts rely on searching for the razor node by mac
address. A previous script changed match_nodes_on to just serial to
avoid duplicate nodes when a server boots off multiple nics. This
commit adds mac as another match_nodes_on parameter so that it can be
searched. Servers should still be considered unique by serial number.
Merge pull request #33 from gavin-scott/add-mac

add mac back to match_nodes_on so it can be searched