Ensure contrib/devstack/install.sh works from any path
Ensure contrib/devstack/install.sh works from any path

Change-Id: I56af596488a2774e8426853550823d88759904e0

tonyli71/designate,openstack/designate,tonyli71/designate,grahamhayes/designate,cneill/designate,kiall/designate-py3,cneill/designate,muraliselva10/designate,kiall/designate-py3,kiall/designate-py3,ionrock/designate,melodous/designate,openstack/designate,grahamhayes/designate,tonyli71/designate,openstack/designate,kiall/designate-py3,melodous/designate,ramsateesh/designate,ionrock/designate,cneill/designate,ramsateesh/designate,cneill/designate,melodous/designate,grahamhayes/designate,kiall/designate-py3,melodous/designate,cneill/designate-testing,muraliselva10/designate,ionrock/designate,cneill/designate-testing,cneill/designate,cneill/designate-testing,ramsateesh/designate,muraliselva10/designate