* Support setting root disk synchronization mode
Adds a new VMConfig parameter (tart get / tart set) called 'sync' which
can be set to 'full' (default), 'fsync', or 'none', corresponding with
the values of VZDiskImageSynchronizationMode and allowing a tradeoff
between data integrity and speed.
* Remove unused import
* Fix formatting
* Make root disk sync behaviour a commandline option
