Don't truncate osapi_glance_link or osapi_compute_link prefixes

When osapi_glance_link_prefix or osapi_compute_link_prefix is
defined and used to update the links return in API responses, do
not drop the path component of the overriding link prefix.

Change-Id: I290e3f85b94e28d25a54621c1699081cbbf48456
Closes-Bug: 1304099
Merge "Don't truncate osapi_glance_link or osapi_compute_link prefixes"