Monasca defaults to using the public endpoint to register
Monasca endpoints which is bad practice and doesn't work on
some deployments. This change uses the admin interface by
default.

Change-Id: Ia9c5e041e71867fe72aad43e1344cd2107652d7d
Co-Authored-By: Mark Goddard <mark@stackhpc.com>
Closes-Bug: #1787610