grid/utils: set PYTHONNOUSERSITE

When PYTHONNOUSERSITE environemnt variable is set, python does not load user
site.
User site packages may contain a different version of buildout, which would
be selected when slapos runs buildout, causing unexpected behaviours.
24 jobs for fix/user-site-packages in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:15:58

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:12:48

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:59:43

failed SlapOS.Eggs.UnitTest-Jerome.Python2

00:16:04

failed SlapOS.Eggs.UnitTest-Jerome.Python2

00:30:28

failed SlapOS.Eggs.UnitTest-Jerome.Python2

00:02:37

failed SlapOS.Eggs.UnitTest-Jerome.Python2

00:00:30

failed SlapOS.Eggs.UnitTest-Jerome.Python2

failed SlapOS.Eggs.UnitTest-Jerome.Python2

passed SlapOS.Eggs.UnitTest-Jerome.Python2

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:12:33

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:16:44

passed SlapOS.Eggs.UnitTest-Jerome.Python2

00:21:53

failed SlapOS.Eggs.UnitTest-Jerome.Python2

00:13:09

failed SlapOS.Eggs.UnitTest-Jerome.Python2

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:08:25

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:25:33

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:11:38

created SlapOS.Eggs.UnitTest-Jerome.Python3
passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:13:40

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:16:41

failed SlapOS.Eggs.UnitTest-Jerome.Python3

00:11:30

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:24:30

passed SlapOS.Eggs.UnitTest-Jerome.Python3

00:17:41