bootstrap: Introduce force_update param for create_config_files()

When running the automated regression tests on autotest,
it is useful to force update of the config files. So,
add this option to the create_config_files function,
so we can make programs that use it.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Add update_config.py script

So that we can upgrade forcefully all config files for
a given test, useful for automated regression testing
of virt-tests.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>