Add a grace period for idle runners of 5 minutes. A new idle runner will
not be taken into consideration for scale-down unless it's older than 5
minutes. This should prevent situations where the scaleDown() routine
that runs every minute will evaluate candidates for reaping and
erroneously count the new one as well. The in_progress hooks that
transitiones an idle runner to "active" may arive a long while after the
"queued" hook has spun up a runner.
Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>
43d2fd8c2d