improvments and bug fixes in devstack to:

1) better handle floating ip address creation
2) not adding the gateway ip address to br-ex
3) keystone endpoint update (first delete then add)
4) keystone public address for public url endpoiint
5) moving re-installing keystone and glance clients just before launching service
6) fixing a problem in swift endpoint change
7) fixing branchs of nova and quantum client in stackrc