use serial number for node uniqueness checks

The default behavior of using mac address to determine node uniqueness
results in duplicate nodes for servers with multiple nics configured
to PXE boot.
Merge pull request #31 from VictorLowther/full-windows-2008r2-support

Allow Freedom of Choice (tm) w.r.t Windows 2008 R2
Merge pull request #32 from gavin-scott/use-serial

use serial number for node uniqueness checks
Add a very basic driver injection script for Windows 2008 pre R2.
Fix some bad powershell syntax