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 commit 'refs/changes/83/86083/2' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch