Bug 9062 Fix format for discount rate for vendors

Bug 9062 Fix format for discount rate for vendors

On the vendor display and edit screens, the tax rate information was
formatted to 1 decimal point, while the discount rate was not.

This patch adds a format string to the discount information so that
it is formatted in the same way.

Signed-off-by: Hugh Davenport <hugh@davenport.net.nz>
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Makes display on vendor detail page more consistent and
passes all tests.
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>