[ubuntu] Rename build scripts (#8866)

* [ubuntu] Rename build scripts

* [ubuntu] Change reboot to inline shell

* [ubuntu] Move disk space validation to pester tests

* [ubuntu] Rename helper and tests files

* [ubuntu] Changes to cleanup, post-deployment and r scripts

images.CI/linux-and-win/build-image.ps1

@@ -50,7 +50,6 @@ packer build    -var "client_id=$ClientId" `
                 -var "virtual_network_name=$VirtualNetworkName" `
                 -var "virtual_network_resource_group_name=$VirtualNetworkRG" `
                 -var "virtual_network_subnet_name=$VirtualNetworkSubnet" `
-                -var "run_validation_diskspace=$env:RUN_VALIDATION_FLAG" `
                 -color=false `
                 $TemplatePath `
         | Where-Object {