Adds XenServer 7.0 (dundee)

src/xenserver.ipxe

@@ -10,6 +10,7 @@ clear osversion
 set os Citrix XenServer
 menu ${os} 
 item --gap Stable Releases
+item 7.0.0 ${space} ${os} 7.0 (dundee)
 item 6.5.0 ${space} ${os} 6.5 (creedence)
 choose xs_version || goto hypervisor_menu
 goto determine_type