Rename python2 subpackage to graphviz-python2
    
    In https://src.fedoraproject.org/rpms/graphviz/c/1b33b027fa547b69d87502b7b20f606898efd9d0?branch=master
    the python2 subpackage was renamed from graphviz-python to
    python2-graphviz. It turns out that there's a separate python-graphviz
    project, so the names conflict. Let's rename the graphviz subpackage
    back to graphviz-python2. Other packages already depend on the python2-graphviz
    name. They will have to be adjusted to use something different.
    Provides: python2dist(gv) is added to graphviz-python2 to make it
    easier for packages which need this module despite the name changes.