Add a script to generate Python bundled provides

See https://src.fedoraproject.org/rpms/python-setuptools/pull-request/40

Strictly speaking, this is not an RPM generator, but:

 - it generates provides
 - it is tighly coupled with pythondistdeps.py

Usage:

 1. Run `$ /usr/lib/rpm/pythonbundles.py .../vendored.txt`

 2. Copy the output into the spec as a macro definition:

    %global bundled %{expand:
    Provides: bundled(python3dist(appdirs)) = 1.4.3
    Provides: bundled(python3dist(packaging)) = 16.8
    Provides: bundled(python3dist(pyparsing)) = 2.2.1
    Provides: bundled(python3dist(six)) = 1.15
    }

 3. Use the macro to expand the provides
 4. Verify the macro contents in %check:

    %check
    ...
    %{_rpmconfigdir}/pythonbundles.py src/_vendor/vendored.txt --compare-with '%{bundled}'

tests/data/scripts_pythonbundles/pkg_resources.in

@@ -0,0 +1,4 @@
+packaging==16.8
+pyparsing==2.2.1
+six==1.10.0
+appdirs==1.4.3