The flag --min-reboot-period can be used to define the minimal duration
between reboots of a node.

Signed-off-by: leonnicolas <[email protected]>

 - only warn on misconfiguration
 - use `node.Annotations` not `node.GetAnnotations()`
 - explicitly check `annotate-node` value before reading an annotation

Signed-off-by: leonnicolas <[email protected]>

If we should not reboot because the last successful reboot is within the
`min-reboot-period`, log the soonest reboot time.

Note, this will also log an error if we cannot determine the last
successful reboot time. However this error is expected when running
kured for the first time with `--min-reboot-period`. The
`last-successful-reboot` annotation will be added to the node after the
first reboot with this feature enabled and then only unexpected error
should be logged.

Signed-off-by: leonnicolas <[email protected]>

Use the `RebootBlocker` interface to implement the min-reboot-period
feature.

Signed-off-by: leonnicolas <[email protected]>