qa: test zero size xattr

Signed-off-by: Yan, Zheng <zyan@redhat.com>
0.90
Merge pull request #3199 from ceph/wip-qa-empty-xattr

qa: test zero size xattr

Reviewed-by: John Spray <john.spray@redhat.com>
Merge remote-tracking branch 'gh/next'
doc/release-notes: v0.90

Signed-off-by: Sage Weil <sage@redhat.com>
working
Merge remote-tracking branches 'athanatos/wip-8635' and 'upstream/master' into wip-sam-working2