Currently, the Neutron gate has two jobs failing consistently.
gate-rally-dsvm-neutron-neutron-ubuntu-xenial has already a fix
available but due to grenade job, it can't be merged.
grenade-dsvm-neutron-dvr-multinode will need to backport patches to pike
so in order to fix the jobs one by one, we'll disable the grenade until
we have a proper fix.
Change-Id: Ibef3812ba9dd67b32918452c7324f660c8e41d6d
Related-bug: #1714901
Related-bug: #1713927