Add LastSeenBuddyBuild to prevent Diagnostics pop up on 10.10.1

When using 10.10.1 as a base DMG, the diagnostics pop up appears during netboot
This appears to be because the key LastSeenBuddyBuild needs to be present in the com.apple.setupAssisstant.plist and needs to contain the os build version

http://derflounder.wordpress.com/2014/11/18/automatically-suppressing-the-icloud-and-diagnostics-pop-up-windows-with-casper/