Fix cells JSON example

The previous cells JSON example was wrong. This patch
updates it to be the same as that in etc/nova/cells.json
from the nova codebase.

Change-Id: I0d692edd11a5a3921fc7b2f9e463899984277df6
Closes-Bug: 1240800
Add list of VIF models for vmware to image doc

As of Havana, VMWare can honor the hw_vif_model properly.

This patch adds the list of supported models so it is now
in line with other hypervisors.

Change-Id: I435b4cb440038a0c3e98685d81ac39251c0cf715
Closes-Bug: 1192639
Merge "Fix cells JSON example"
Merge "Add list of VIF models for vmware to image doc"