Witold Kręcicki authored Oct 09, 2019 and Matthijs Mekking committed Nov 06, 2019

When doing regular signing expiry time is jittered to make sure
that the re-signing times are not clumped together. This expands
this behaviour to expiry times of dynamically added records.

When incrementally re-signing a zone use the full jitter range if
the server appears to have been offline for greater than 5 minutes
otherwise use a small jitter range of 3600 seconds.  This will stop
the signatures becoming more clustered if the server has been off
line for a significant period of time (> 5 minutes).

(cherry picked from commit 6b2fd402)