common: add helpers for parent pointer tests

common: add helpers for parent pointer tests

Add helper functions in common/parent to parse and verify parent
pointers. Also add functions to check that mkfs, kernel, and xfs_io
support parent pointers.

Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: add license and copyright, dont _fail tests immediately, make
 sure the pptr-generated paths match the dir-generated paths]
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>