Rationalize supplement and openstack repo URLs

The parameters for the Cisco supplemental repo URL and
the Cisco main OpenStack repo are specified slightly differently:
the Cisco supplemental repo is provided as the full URL to the
root of the repository.  The main repo, however, is specified
as a URL that isn't quite complete and a static string '/cisco'
is then added to the end within the class.  This is inconsistent
and makes it more difficult to re-use the hiera params that set
these up in other classes.  This commit rationalizes the two
by changing the default for the Cisco main URL to include
the trailing '/cisco' and removes the static addition from the
later code.

Partial-Bug: #1269856