Versions links are wrong when behind a proxy changing path

When behind a proxy changing the path to the Blazar API, the links returned in the versions response are incorrect. This is the case with the default DevStack configuration which uses the ProxyPass directive.

$ http GET http://10.0.0.149/reservation X-Auth-Token:$OS_AUTH_TOKEN
HTTP/1.1 300 Multiple Choices
Connection: close
Content-Type: application/json
Date: Wed, 11 Sep 2019 12:52:13 GMT
Server: Apache/2.4.6 (CentOS) OpenSSL/1.0.2k-fips mod_wsgi/3.4 Python/2.7.5
Transfer-Encoding: chunked

{
    "versions": [
        {
            "id": "v1.0",
            "links": [
                {
                    "href": "http://10.0.0.149/v1",
                    "rel": "self"
                }
            ],
            "max_version": "1.0",
            "min_version": "1.0",
            "status": "CURRENT"
        },
        {
            "id": "v2.0",
            "links": [
                {
                    "href": "http://10.0.0.149/v2",
                    "rel": "self"
                }
            ],
            "status": "DEPRECATED"
        }
    ]
}

The links should be to http://10.0.0.149/reservation/v1 and http://10.0.0.149/reservation/v2.

Keystone and Glance both have a `public_endpoint` configuration value which they use to build the correct URL.