The attached file is gnu/services/trytond.scm which successfully runs trytond.
I run it and I confirm it works
I couldn't attemp at installing a couple of Tryton modules (on top of the base ones) because in the vm the keyboard layout is messed up and I couldn't use the command line properly (in the xfce terminal)
I tried to set it up with the xfce panel, but it's not so immediate, so I gave up
I'd merge this patch anyway, I'd keep working on Tryton/GNUHealth fron the next reconfigure onwards