Fixes#1473.
writes privkey.pem to 0600 by default for new lineages
on renewals where a new privkey is generated, preserves group mode and gid
Things this PR does not do:
we talked about forcing 0600 on privkeys when a Certbot upgrade is detected. Instead, this PR only creates new lineages with the more restrictive permission to prevent renewal breakages.
this doesn't solve many of the problems mentioned in #1473 that are not directly related to the title issue!
* safe_open on archive keyfiles
* keep group from current lineage
* clean up integration test
* safe_open can follow symlinks
* fix tests on windows, maybe
* Address Brad's comments
* Revert changes to safe_open
* Test chown is called when saving new key
* Reorder chown operation
* Changelog and documentation
* Fix documentation style
7d0ac47139