Shaper::Set: rollback
Shaper::Unset: rollback
Shaper::Change: rollback
Shaper::RootChange: rollback
Vps::ApplyConfig: rollback

Original config is backed up and restored if necessary. This solution
is not that perfect, because CT may have some changes in configuration
which will be reverted only after the CT is restarted.
Vps::Mount and Umount: rollback
Vps::Mounts: rollback

Original action scripts are backed up and restored if necessary.
Vps::DnsResolver: rollback
Vps::Hostname: rollback
Vps: applyconfig moved to command itself
Command: fix single transaction rollback