add 059 and 060 to test multi-stream xfsdump

add 059 and 060 to test multi-stream xfsdump

Implement the multi-stream placeholder tests 059 and 060. The comments
imply that these tests existed on IRIX, but I was unable to find them.

Test 059 does a simple 4-way dump and restore. Test 060 does a 4-way
dump, then restores each dump file individually (in a cumulative
fashion).

The tests are skipped if the installed xfsdump does not support
multi-stream output.

Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Bill Kendall <wkendall@sgi.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>