common: fix flink check

common: fix flink check

I don't have flink support in my xfsprogs, but it doesn't fail with "command not
found" or whatever, it fails because I don't have the -T option, whereas Eric
gets an error about $TEST_DIR being a directory because his xfs_io tries to open
the directory first before it parses the options.  So fix this by checking flink
with these two cases and don't run if we hit either of them.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>