Update to 0.9.155, fix tests with Python 3.6 and lxml 3.7
    
    Fixes submitted upstream. Note on the change from `rm -r` to
    `rm -rf`: there is a directory named `test` nested in another
    directory named `test` (`pcs/test/tools/test`). Depending on
    the order in which they're found, `rm -r` might wind up trying
    to remove `pcs/test/tools/test` after `pcs/test`, which is an
    error and causes %check to fail. `rm -rf` ignores missing
    targets, so it succeeds even in this scenario.