Do not install openvswitch-datapath-dkms on Ubuntu 14.04

Change-Id: I8c58d998011427a202c79c45b87b5eca5ceaaa71
Closes-bug: #1331111
Merge "Do not install openvswitch-datapath-dkms on Ubuntu 14.04"
Merge branch 'master' of github.com:openstack-dev/devstack