dgit-mirror-ssh-wrap: Cope with new rsync rune

rsync 3.2 passes -I and -v to the remote process.  These options are
no problem.

Rather than making this into an single mess of a regexp, add a new
regexp for the new rune.  That's clearer and I think probably just
about as future-proof.

Closes: #963489
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>