cleanup: Driver.generateDiskImage() duplicated in multiple drivers

[nirs]

This function should move to common location and reused by drivers instead of duplicating it the driver.

• qemu:

  minikube/pkg/drivers/qemu/qemu.go

  Line 691 in b973335

  func (d *Driver) generateDiskImage(size int) error {

• vfkit:

  minikube/pkg/drivers/vfkit/vfkit.go

  Line 492 in b973335

  func (d *Driver) generateDiskImage(size int) error {

• krunkit:

  minikube/pkg/drivers/krunkit/krunkit.go

  Line 465 in b589890

  func (d *Driver) generateDiskImage(size int) error {

Originally posted by @medyagh in #20826 (comment)