xfs_io: make various commands one-shot only

xfs_io: make various commands one-shot only

It makes no sense to iterate the file table for some xfs_io
commands. Some commands are already marked in this way, but lots of
them are not and this leads to bad behaviour. For example, the open
command will run until the process fd table is full and EMFILE is
returned rather than just opening the specified file once.

Signed-Off-By: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>