customization: UX for VM disk size

Change-Id: I52f3a6a9370511b63c589eb0537a237e51aa5046
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
customization: UX for VM memory size

Change-Id: I78364f0f57e00c6f2a08d4c19af4ad4d59b05dd4
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>