test_updater.py: more robuste approach, independent from unique ids
test_updater.py: more robuste approach, independent from unique ids

this should make the test reproducible on different machines, no matter the
order in which tuples are inserted (and hence of the order in which postgres
generates unique ids)

drawback: we now hardcode per-table queries that are granted to be stable. This
is, de facto, duplication of the DB design between models.py and
test_updater.py

as a side-effect of this change: port test_updater.py to the new DB structure,
post refactoring of the files table

vivekanand1101/debsources,sophiejjj/debsources,devoxel/debsources,sophiejjj/debsources,matthieucan/debsources,nonas/debian-qa,nonas/debian-qa,Debian/debsources,vivekanand1101/debsources,zacchiro/debsources,sophiejjj/debsources,devoxel/debsources,sophiejjj/debsources,devoxel/debsources,Debian/debsources,oorestisime/debsources,vivekanand1101/debsources,zacchiro/debsources,devoxel/debsources,vivekanand1101/debsources,clemux/debsources,matthieucan/debsources,nonas/debian-qa,zacchiro/debsources,devoxel/debsources,matthieucan/debsources,matthieucan/debsources,zacchiro/debsources,vivekanand1101/debsources,zacchiro/debsources,clemux/debsources,oorestisime/debsources,sophiejjj/debsources,oorestisime/debsources,oorestisime/debsources,matthieucan/debsources,clemux/debsources,Debian/debsources,Debian/debsources,clemux/debsources,oorestisime/debsources,clemux/debsources,nonas/debian-qa,Debian/debsources