Configure the OVS datapath type with devstack.

This feature provides the user with a means of easily configuring
the required Openvswitch datapath type. (Netdev, dpdk, etc)

Define the OVS_DATAPATH_TYPE variable in the devstack configuration file
local.conf.

This feature enables Intel(R) DPDK vSwitch and netdev DPDK vhost.

Implements blueprint config-ovs-datapath-type

Change-Id: I5698720960b1ac532c790d3e5735c5cef36d5e3d
Merge "Configure the OVS datapath type with devstack."