stack/erp5: handle coverage reporting from erp5.git

This now supports producing html reports directly
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed Cloudooo.UnitTest-Master

00:38:26

passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

00:49:21

passed SlapOS.Eggs.UnitTest-Master.Python2

00:30:15

passed SlapOS.Eggs.UnitTest-Master.Python3

00:31:05

passed SlapOS.Eggs.UnitTest-Master.Python3Next

00:21:04

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

00:58:34