Include information on the routing of metadata requests

This helps administrators to adapt the configuration to their
installation.

Change-Id: Ibaace65787d8572837316cde1570c31dd1df3ffc
Use build_file_exception for ha-guide-docinfo

openstack-doc-test 0.9 adds one more option, prepare the config file for
it.

Change-Id: Ib68b8702206939096c10d7196d5c6fed4d005376
Merge "Include information on the routing of metadata requests"