Revert "kvm: Implement external-disk"

This reverts commit e7b48c0b.
8 jobs for 1.0
Status Job ID Name Coverage
  External
failed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

failed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch

failed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Buster

failed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Stretch

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Stretch