handle buildout `allow-picked-version` value

If deployment mode option is not provided, default
value is `not allow-picked-version`.
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:18:56

passed SlapOS.Eggs.UnitTest-Master.Python3

00:21:54

passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:15

passed SlapOS.Eggs.UnitTest-Master.Python3

00:26:03

passed SlapOS.Eggs.UnitTest-Master.Python3

passed SlapOS.Eggs.UnitTest-Master.Python3