Promote check-grenade-dsvm-neutron to voting job

After https://review.openstack.org/#/c/134484 is merged we should make
neutron grenade job voting in order to avoid breakage of this job in the
future.

Change-Id: I1b3d2d30479f1a51d534a48d815b84ce1ed5f317
Merge "Promote check-grenade-dsvm-neutron to voting job"