qemu-img: Make documentation between .texi and .hx consistent

These are also different and out of order for whatever reason.
I'd like to automate this in the future, but for now let's put
on the band-aid.

In the case of resize, there were options missing from all
three docstrings; the new string is based on the code.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>