nmcli/devices: add "checkpoint" command
This is an interface to the Checkpoint/Restore functionality that's available for quite some time. It runs a command with a checkpoint taken and rolls back unless success is confirmed before the checkpoint times out: $ nmcli dev checkpoint eth0 -- nmcli dev dis eth0 Device 'eth0' successfully disconnected. Type "Yes" to commit the changes: No Checkpoint was removed. The details about how it's used are documented in nmcli(1) and nmcli-examples(7).