[Continuous] Work around SSL issue with ostree admin upgrade

[Colin Walters <walters verbum org>]

Hi, a notice for Continuous users:

https://git.gnome.org/browse/ostree/commit/?id=f60bac45fdf9e9b1b8f663f859ffdee190f2fd0c
regressed ostree in Continuous; you will see "Unacceptable TLS
certiifcate" when doing
"ostree admin upgrade".

This is the fix:
https://git.gnome.org/browse/ostree/commit/?id=772409e945aa1f5d8e6c20c233fa36dda80950d8

To work around it, edit
/ostree/repo/config, and change https:// to http://, do an upgrade, then
change it back, then
reboot.