fixup! erp5testnode: clean up old instance root folder

With software release test suites, there are probably
files/folders with permission issues.

See commit 380037f8.
14 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:08:49

passed ERP5.PerformanceTest-Master

00:23:54

failed ERP5.UnitTest-Master

01:45:05

failed ERP5.UnitTest-Master.Medusa

02:32:13

passed SlapOS.Eggs.UnitTest-Master.Python2

00:57:28

failed SlapOS.Eggs.UnitTest-Master.Python3

00:09:38

failed ERP5.UnitTest-Master

03:56:26

failed ERP5.UnitTest-Master

failed ERP5.UnitTest-Master

passed SlapOS.Eggs.UnitTest-Master.Python2

00:32:01

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python2

00:18:10

failed SlapOS.Eggs.UnitTest-Master.Python3

00:18:50

failed SlapOS.Eggs.UnitTest-Master.Python3

00:09:13