If cluster verification in Sahara is totally disabled, then operators
probably do not want to have ugly UNKNOWN in the cluster status page.
They also probably do not want any references to health at all, if
there will never be any usable information there. So, let's add
something that can be read from local_settings to disable these when
the operator doesn't want them.
Change-Id: Ifc624d07767ed29646aa8a5b5739103fd4972b90
Co-Authored-By: Lucas H. Xu <xuh@bu.edu>