common: fix _count_extents and _count_holes

common: fix _count_extents and _count_holes

In _count_extents and _count_holes, the output of 'xfs_io -c "fiemap"'
is saved in var res, but the following "echo $res" will merge the
original output into one line. e.g.

	0: [0..63]: 96..159
	1: [64..127]: hole

will be

	0: [0..63]: 96..159 1: [64..127]: hole

so the extent count is always 0 if there's a hole.

This makes generic/046 fail occasionally. (Seems it's easier to
reproduce when the system is under some presure, e.g. with fsstress
running.)

Tested the new _count_extents and _count_holes with generic/04[3-9] and
tests all passed as expect.

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