This will fix exit codes - details in bug.

Basically openvswitch treats TERM as something fatal (exits
with 143) and the only solution for graceful exit is using
ovs-appctl and sending exit command, just like ovs-ctl utility
does.

Depends-On: https://review.opendev.org/c/openstack/kolla/+/905189

Partial-Bug: #2048130
Change-Id: I523018cb98944de60d7b95404deb7cebd641f33a