Use the same mender-artifact version that the docker method
Use the same mender-artifact version that the docker method

Using master for tests and latest stable for Docker will always lead to
problems when incompatible releases are in the making.

Changelog: None

Signed-off-by: Lluis Campos <9244cb41c39addfc5cf236920b776ea2820513d0@northern.tech>

mendersoftware/meta-mender-qemu