testXHTML: retry on ConnectionError as well

Such errors are not retried with the retry adapter, so retry them
directly.
16 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

01:38:25

passed ERP5.UnitTest-Master

02:56:55

failed ERP5.UnitTest-Zope2

02:24:37

passed SlapOS.Eggs.UnitTest-Master.Python2

00:22:57

passed SlapOS.Eggs.UnitTest-Master.Python3

00:17:49

passed Wendelin.UnitTest-Master

01:02:15

passed ERP5.CodingStyleTest-Master

01:03:18

passed ERP5.CodingStyleTest-Master

01:21:17

failed ERP5.UnitTest-Master

01:55:11

failed ERP5.UnitTest-Zope2

01:44:58

passed SlapOS.Eggs.UnitTest-Master.Python2

00:14:15

passed SlapOS.Eggs.UnitTest-Master.Python2

00:20:16

passed SlapOS.Eggs.UnitTest-Master.Python3

00:17:21

passed SlapOS.Eggs.UnitTest-Master.Python3

00:16:45

failed Wendelin.UnitTest-Master

00:50:48

failed Wendelin.UnitTest-Master

01:09:19