use latest AKS VHD (#4074)
use latest AKS VHD (#4074)


Azure/acs-engine,Azure/acs-engine,jackfrancis/acs-engine,jackfrancis/acs-engine,Azure/acs-engine,jackfrancis/acs-engine,jackfrancis/acs-engine,Azure/acs-engine,jackfrancis/acs-engine,Azure/acs-engine