
df --output was new in coreutils 8.21 (2013), and non-GNU implementations like busybox df don't have it. This avoids a test failure in Steam Runtime 1 'scout', which is based on Ubuntu 12.04 (2012). It'll also be helpful for anyone maintaining an OS with non-GNU shell utilities. Signed-off-by: Simon McVittie <smcv@collabora.com>