devstack: call odl-ovs-hostconfig conditionally
devstack: call odl-ovs-hostconfig conditionally

neutron-odl-ovs-hostconfig requires ovs 2.5+.
On the other hand, openstack CI with ubuntu-trusty includes older
ovs version.
So invoke neutron-odl-ovs-hostconfig only when pseudo-agentdb-binding
is specified. Otherwise don't call it because it's not necessary.

Change-Id: Ic58b91252b68d5d66d18ff09ae44ced8669ec815
Closes-Bug: #1632873

openstack/networking-odl,openstack/networking-odl,openstack/networking-odl