VMware: spawn refactor - phase 1 - power_on_vm

move power_on to vm_util and change all power_on in vmops to use it

ensure test_driver_api tests only the driver and not vmops

change id for the last review in this phase 1 series with a spawn
test is Ia137f1ea4b9fa43741cdd7d610831da8e5474d62

partial blueprint vmware-spawn-refactor

Change-Id: I5c1d8bc38c4a7d0107c8d7639e385239e53b070d
VMWare: spawn refactor - phase 1 - create_virtual_disk

Several methods are repeating code for creating the virtual disk.
This refactor isolates the code for that task so it can be reused.

partial blueprint improve-vmware-disk-usage
partial blueprint vmware-spawn-refactor
Co-authored-by: Maithem <munshedm@vmware.com>
Co-authored-by: Tracy Jones <tjones@vmware.com>

Change-Id: If764340be76abbb24e1954f02b3ecb317ba143f9