dpdk-vswitchd: some ovs tools require ovs daemons pidfiles

Change-Id: I797bb5997e6a3391e82bff766c96f7855de4adc4
Closes-bug: #1878325

ansible/roles/ovs-dpdk/templates/ovsdpdk-vswitchd.json.j2

 {
-    "command": "/usr/sbin/ovs-vswitchd unix:/run/openvswitch/db.sock -vconsole:emer -vsyslog:err -vfile:info --mlockall --log-file=/var/log/kolla/openvswitch/ovs-vswitchd.log",
+    "command": "/usr/sbin/ovs-vswitchd unix:/run/openvswitch/db.sock -vconsole:emer -vsyslog:err -vfile:info --mlockall --log-file=/var/log/kolla/openvswitch/ovs-vswitchd.log --pidfile",
     "config_files": []
 }