update aks ubuntu version to 2020.04.16 (Azure#3092)

Co-authored-by: Adil Adilli <adadilli@microsoft.com>

switch to use the 04.13 image which contains the cve patch. (Azure#3078)

feat: EncryptionAtHost support (Azure#3064)

fix missing part

fix: retry more aggressively when install the gpu deb package. (Azure…

…#3065) (Azure#3068)

Use VHD 2020.04.12

fix: make sure nvidia utility and compute bins can be mounted into co… (

Azure#3029)

bump the vhd version which contains the route table hotfix. (Azure#3036)

chore: rev Linux VHDs to 2020.03.19 (Azure#2939)

feat: updating windows VHD for Feb k8s versions (Azure#2731)

fix: enable upgrade in private cluster + jumpbox scenario (Azure#2634)