Use slapos.core with python3

The egg slapos.core is now used with python3 by default (except in slaprunner).

See merge request !1154
10 jobs for django-tutorial in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:23:40

passed SlapOS.Eggs.UnitTest-Master.Python3

00:23:20

passed SlapOS.SlapRunner.ResilienceTest-Master

00:22:12

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

01:31:44

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

08:53:27

passed SlapOS.Eggs.UnitTest-Master.Python2

00:16:01

passed SlapOS.Eggs.UnitTest-Master.Python3

00:31:29

passed SlapOS.SlapRunner.ResilienceTest-Master

00:29:22

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

01:28:21

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master