README/devstack: fix spurious space in IPVPN driver specification
README/devstack: fix spurious space in IPVPN driver specification

(plus cosmetic re-indentation)

Change-Id: I8e3ac4e7a13b2e83731faf3062f457aa88bcef8d

openstack/networking-bgpvpn,openstack/networking-bgpvpn,openstack/networking-bgpvpn