Add default configuration for `resultsdir`
    
    Rpkg added support for new configuration option `resultsdir` in [1].
    Default configuration is set: `git_exclude` to exclude the new
    `results` directory, and `resultsdir` option set of `root`, in order to
    preserve the current behavior by default and make the new `subdir`
    option opt-in.
    
    [1]: https://pagure.io/rpkg/c/89bc57df4f2dcc22004c3e412df3013b62b70ffb?branch=master
    
    Signed-off-by: Otto Urpelainen <oturpe@iki.fi>
    Merges: https://pagure.io/fedpkg/pull-request/432