It's not needed at all so if we avoid installation, especially from
sources, it may save us few minutes of the job's execution time.
It may also save some resources on the node.
To save a bit more time in the fullstack job's execution this patch also
disables compilation of the OVS from source in that job. We can use OVS
installed from packages provided by the distro instead.
Change-Id: Ic4b6740671e51f0d306967013e3d500f4d0cd6a5