Correct URIs in version information returned at /

The root / endpoint for Keystone returns a JSON dict
of information about the versions supported by Keystone.
This dict of information contained bad URIs, which I suspect
is preventing the v3 API from being navigated through by clients
who parse this version dictionary.

The public_endpoint and admin_endpoint configuration options
need a URI without any version path in it.

Change-Id: Ib8bf1d1f95bd86afa2a327e1cff011de8d3039f4