Currently we're developing a new in-band deduplication feature for btrfs,
when enabing this feature, it will take much long time to hit the enospc
condition which 275 tries to create. I think 275 is also certain enospc
test and we should add it to 'enospc' group, then we can skip it easily by
excluding 'enospc' group when running fstests.
Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>