Allow passing --offline and -r to mbs-manager build_module_locally.
    
    It is now possible to build modules offline without any external
    infrastructure using the MBS. This is done by passing `--offline`
    flag to mbs-manager and the list of repositories for the base
    module.
    
    In this commit, the support for these new flags (`--offline` and `-r`)
    is added to pyrpkg.
    
    Signed-off-by: Jan Kaluza <jkaluza@redhat.com>