Add sudoers rule to format and mount anykind of partitions in disks.

The element vm is the only one creating a partition in the disk.
If not included, it will ask for sudo password to format or mount
the whole nbd disk or disks with multiple partitions.

Change-Id: Iac0987d2088433873b7cbb68deecc9254b2d0103
Merge "Add sudoers rule to format and mount anykind of partitions in disks."