Following this commit[1], bind_host has been moved to public_bind_host
letting admin_bind_host undefined, hence trying to bind to 0.0.0.0.
Since HAProxy already listens on an IP address it prevents the keystone
service from starting.
[1] 9bf5e54f5c95dc5b610ebba9958c6f3ae1f77a13
Change-Id: I942c473e9c0ad7dcd61f10339cadddcda01e7c7b