[RFE] use NetworkManager's Checkpoint feature to rollback on error

[thom311]

NetworkManager's Checkpoint feature allows to record the current configuration (snapshot), together with a timeout. Commonly, the user/script then would go ahead and change the networking configuration. If the timeout expires without the checkpoint being expired, the configuration of the snapshot is restored. The user can also manually issue a rollback before the timeout expires, or just cancel the timeout (in which case the snapshot is forgotten).

This can be used for two cases:

• if the module operates and notices an issue in the middle of the operation, it can manually issue a rollback to restore the previous (working) setup.
• if the module succeeds, but the user is unable to reach the host afterwards -- that is, the new configuration cut the host off the network -- then the role won't be able to cancel the checkpoint, and the timeout will hit -- to restore the previously working configuration.