Add helper for poll/sleep loops with timeout
The Sleeper class is a helper that makes poll/sleep loops with timeout
easier to write. It takes care of edge cases and does not oversleep
timeout deadline.
Related: https://pagure.io/freeipa/issue/8521
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>