Change default bond-mode

Change default bond-mode

The default balance-tcp is causing issues with deployments.
Defaulting to active-backup.

After ~ 100 guests (total) connectivity to each guest would become spotty
(simple pings would fail, then become successful.) In /var/log/messages
we saw :
"overcloud-controller-1 kernel: openvswitch: ovs-system: deferred action
limit reached, drop recirc action"

For more details, refer to this link:
http://openvswitch.org/pipermail/discuss/2015-October/019168.html

Change-Id: Ia0f2592a289e13472b98d97057cd516c5048fe59