Use neutron-legacy on subnodes in devstack zuul job

There are still some issues with lib/neutron thus neutron-legacy is used
on controller node in multinode jobs and in single node jobs.
But in "group-vars" in devstack job it was configured to use
lib/neutron which can cause some problems in multinode jobs.

So lets switch to neutron-legacy on subnodes also until lib/neutron
will be ready to use everywhere.

Change-Id: I0d7f9f2baaee2836a719f199939156bd4f53f778
1 file changed