Adding barcodes back into the GeneratorObjects and GeneratorObjectsTPCnv unit tests.
This will become important as the barcode migration (ATLASSIM-6906) continues and we need to confirm that legacy persistent formats are treated correctly.
NB As the migration progesses barcode support will be dropped from McEventCollection_p7 and
a barcode-independent HepMcParticleLink_p3 will be introduced.