Diskbus config


It provides config option to override disk_bus configuration on box.xml.

User can set disk interface to vertio for box that is defined to use ide/sata as disk interface.
Or it can solve a reverse case.

vagrant-mutate generate kvm box that respect original OVF definition.
User can use it as is and also config disk interface with this.

After successful test, box can be create vagrant package with best disk interface.

retry of #113