Update to use new Coopr API.

Coopr recently deprecated ModelData and are migrating folks to
DataPortal.  Well, deprecated is the wrong word: ModelData simply no
longer works internally to Pyomo.
Bitten by integer division.

This is that subtle, easily missed detail, where 1 / n is 0, if abs(n)
is a natural number greater than 1.  Either of these will return the
correct, expected fraction:

    1. / n
    1.0 / n

Alas.  Fixed.
Change to using soon-to-be Pyomo only API

With the release of Pyomo 4.0, the Coopr libraries are now named only
Pyomo.  This commit follows the Pyomo API per usual.
Missing conversion from Coopr to Pyomo