Update pipeline image to Ubuntu 20.04 (#5066)

.pipelines/e2e-job-template.yaml

@@ -13,7 +13,7 @@ jobs:
   strategy:
     maxParallel: 0
   pool:
-    vmImage: ubuntu-18.04
+    vmImage: ubuntu-20.04
 
   container: dev1
 

.pipelines/pr-e2e.yaml

@@ -26,7 +26,7 @@ jobs:
   strategy:
     maxParallel: 0
   pool:
-      vmImage: 'Ubuntu 18.04'
+      vmImage: 'Ubuntu 20.04'
 
   container: dev1
 

.pipelines/vhd-builder.yaml

@@ -11,7 +11,7 @@ jobs:
   variables:
     CONTAINER_IMAGE:  'mcr.microsoft.com/oss/azcu/go-dev:v1.34.7'
   pool:
-    vmImage: 'Ubuntu 18.04'
+    vmImage: 'Ubuntu 20.04'
   steps:
   - script: |
       docker run --rm \