The test ostree commit is generated after the successful commit.
Removing updatectl, it makes it impossible to mark an update successful.
Hence the bootcount will be increased at each boot, eventually causing
rollback to the previous deployment.

Ostree provides --skip-list that allows to create a commit with a list
of files to skip. That is useful to generate the rollback commit.
This way there is not need to modify existing recipes or provide
additional one. The execution time is also very short.

Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>