Real Apertis images have ~/Documents already, but the Documents
directory isn't created when the filesystem image is picked apart
and reassembled by LAVA. This causes `mktemp`, and hence the
apparmor-libreoffice test, to fail on LAVA.

Relevant to T2104, but does not close it.

Reviewed-by: Luis Araujo <luis.araujo@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D3765