etcd backup failing: can't find juju_id_rsa file

[Paul Goins]

On some environments, the etcd backup fails due to not being able to find the juju_id_rsa SSH key needed to connect to the target machines/VMs.

Partial juju-backup-all output:

2022-02-28 23:14:14,701 INFO jujubackupall.process [foundations-maas] Processing backups.
2022-02-28 23:14:14,709 INFO jujubackupall.process [foundations-maas] Models to process ['controller', 'default', 'openstack']
2022-02-28 23:14:15,093 INFO jujubackupall.process [foundations-maas controller] Backing up apps.
2022-02-28 23:14:15,201 INFO jujubackupall.process [foundations-maas default] Backing up apps.
2022-02-28 23:14:16,251 INFO jujubackupall.process [foundations-maas openstack] Backing up apps.
2022-02-28 23:14:22,840 INFO jujubackupall.process [foundations-maas openstack etcd] Backing up app.
2022-02-28 23:14:23,645 INFO jujubackupall.process [foundations-maas openstack etcd] Downloading backup.
Warning: Identity file /home/jujumanage/snap/juju-backup-all/1/.local/share/juju/ssh/juju_id_rsa not accessible: No such file or directory.
2022-02-28 23:14:23,667 ERROR jujubackupall.process [foundations-maas openstack etcd] App backup not completed: command failed: ['scp', '-i', '/home/jujumanage/snap/juju-backup-all/1/.local/share/juju/ssh/juju_id_rsa', '-o', 'StrictHostKeyChecking=no', '-q', '-B', 'ubuntu@<REDACTED>:/home/ubuntu/etcd-snapshots/etcd-snapshot-2022-02-28-23.14.23.tar.gz', '/home/jujumanage/bootstack-backups/foundations-maas/openstack/etcd'].