Bug 13308: The output format should be 'iso2709' instead of 'marc'

Bug 13308: The output format should be 'iso2709' instead of 'marc'

In the template of the export tools, the value 'marc' is set for
the 'format' variable.
It should be 'iso2709'.

There was a mess in the tools/export.pl script.
2 variables did the same thing: $format and $output_format

This patch fixes that replacing $format with $output_format

Test plan:
Try to export biblio in iso2709 and csv using the export tools and from
the checkout list.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Before applying the patch, attemping an MARC export from tools/export.pl
resulted in an error. After the patch the export works correctly.
Exports from the checkouts page also work correctly.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes tests and QA script. Also tested authority export.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>