Provide a new method 'addMinimalBundleSet()' that adds all bundles from
the MINIMAL_BUNDLE_SET to the suite. It obtains the bundles using a
class from each bundle. This has the advantage that this method does not
rely on fixed bundle names that might change in the future and therefore
simplifies migration.
This has the second positive effect that the o.e.core.tests.harness
plug-in requires all bundles from the MINIMAL_BUNDLE_SET and therefore
automatically pulls them into the test-runtime. This avoids the need for
users to add them 'manually'.

Additionally simplify PlatformURLSessionTest and
ConfigurationSessionTestSuite itself.