Enable l3_ha in neutron config for scenario jobs

This patch sets l3_ha config option in neutron server to be
True in singlenode scenario jobs:
 - neutron-tempest-plugin-openvswitch
 - neutron-tempest-plugin-openvswitch-iptables_hybrid
 - neutron-tempest-plugin-linuxbridge

So all routers created in those jobs will be HA by default.
Even in single node jobs this will provide us better coverage
of L3HA mode for routers becuase we didn't have any job to cover
such case since now.

Depends-On: https://review.opendev.org/c/openstack/neutron/+/776618

Change-Id: I368d0e9410b009097b29367579f958e3ff537936
6 files changed