erp5testnode/testsuite: switch to buildout.hash.cfg

This was missing in this software and in 03c5b311 (Stop using
hexagonit.recipe.download, 2021-12-03) the hash got out of sync
4 jobs for fix/missing-ca-certificates
Status Job ID Name Coverage
  External
failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

01:03:16

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5