Backup uploaded/changed every day

[filippocarletti]

The tar.gz backup file changes every time the backup is run.
Two causes:

1. timestamp of /etc/backup/installed_packages.txt
2. /etc/uci-defaults/10_disable_services

Steps to reproduce

• Run sysupgrade -k -b /tmp/backup1.tar.gz
• Run sysupgrade -k -b /tmp/backup2.tar.gz
• Compare the two backups: md5sum /tmp/backup?.tar.gz

Expected behavior

The backups should be identical (the content is).

Actual behavior

Backups are different.

See also

https://github.com/openwrt/openwrt/pull/16146/files
openwrt/openwrt#16145

[gsanchietti]

Proposed implementation in #1149 can cause many regressions.

As @filippocarletti proposal, let's wait a fix from upstream.

Note: currently the remote backup server can contain up to 2MB of backups or up to 10 archives. Currently, on a normal machine, there is an historical record of 8 backups.