tests: Work around mender.conf setup difference between Yocto branches.
tests: Work around mender.conf setup difference between Yocto branches.

1.7.0 was built with sumo, before mender.conf was split up into a /etc
version and a /data version. Hence the latter variant is missing, and
the new update needs this. So create this file as part of the upgrade
process in the test.

Changelog: None

Signed-off-by: Kristian Amlie <505e66ae45028a0596c853559221f0b72c1cee21@northern.tech>

pasinskim/integration,pasinskim/integration,pasinskim/integration