xfs/262: update filter to deal with long device name correctly

xfs/262: update filter to deal with long device name correctly

If the device name is too long, the output of xfs_quota -c "df" will be
broke into two lines as

Filesystem           1K-blocks       Used  Available  Use% Pathname
/dev/mapper/rhel_hp--dl388eg8--01-testlv2
                      15718400      32932   15685468    0% /mnt/testarea/scratch
/dev/mapper/rhel_hp--dl388eg8--01-testlv2
                        512000          0     512000    0% /mnt/testarea/scratch/test

and _filter_quota_rpt() couldn't catch the correct available number and
test will fail as

	[root@hp-dl388g8-01 xfstests]# diff -u tests/xfs/262.out /root/xfstests/results//xfs/262.out.bad
	--- tests/xfs/262.out   2014-10-08 20:16:19.000000000 +0800
	+++ /root/xfstests/results//xfs/262.out.bad  2014-10-09 14:29:38.795813323 +0800
	@@ -1,2 +1,4 @@
	 QA output created by 262
	 Silence is golden.
	+hard limit 0 bytes, expected 524288000
	+hard limit 0 bytes, expected 524288000

Update the filter so it could catch the correct value.

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>