Oned should check for inconsistencies in disk target names

[dgarcia18]

Description
Currently the user can specify disk target values (sda, vda, vdb, etc.) for the disks attached to a VM. Nonetheless, this value is sometimes not applied inside the Guest OS.

The reason is that inside the Guest OS there are some limitations regarding this labeling:

• Bus: If a disk is using the VirtIO bus, the name will be of the form vdX (e.g. vda). A user should not be able to set a name not preceded by "vd"
• Order: The naming must follow an order. E.g. there can not be a "vdb" if there is no "vda", and there can not be a "sdc" if there is no "sdb".

Oned should have into account these limitations and report an error to the user in case of inconsistencies.

Use case
Improving user experience, specially regarding appliance creation and persistency.

Interface Changes
The error should be showed in all interfaces.

Progress Status

• Code committed
• Testing - QA
• Documentation (Release notes - resolved issues, compatibility, known issues)