generic: test that xattrs can have slashes in their names

generic: test that xattrs can have slashes in their names

Eric Sandeen recently found a bug in xfs_repair that flagged extended
attribute names containing "/" as corrupt and purged them.  There's
nothing in the IRIX or Linux manuals that say anything about slashes not
being allowed (and Linux certainly allows this) so let's make sure this
continues to work.

[Eryu: use $SETFATTR and _getfattr helper]

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>