feat(wsgi): homedoc now ships relative URIs

The document root can be obtained from the service catalog, so
that users can join two URIs to access the doc.

The health endpoint is removed from homedoc at the same time,
since it's an API for diagnose, not for end-users.

Change-Id: I589ff88730302bc553041ecccb9687f7dbcaa9ab
Merge "feat(wsgi): homedoc now ships relative URIs"