Pools can now define a bootstrap timeout for runners. The timeout can
be defined per pool and indicates the amount of time after which a runner
is considered defunct and removed.
If a runner doesn't join github in the configured amount of time, and it
receives no updates indicating that it is installing the runner via instance
status updates, it is considered defunct.
Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>
