slapos_cloud: Keep using older group_id when generate new references

  When upgrade the site, we shouldn't revert the count, else it may lead to duplicated values.
12 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS-Master.UnitTest-Master

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passed SlapOS.Eggs.UnitTest-Master.Python2

failed SlapOS.Eggs.UnitTest-Master.Python3

failed SlapOS-Master.UnitTest-Master

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passed SlapOS.Eggs.UnitTest-Master.Python2

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passed SlapOS.Eggs.UnitTest-Master.Python2

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passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python2

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passed SlapOS.Eggs.UnitTest-Master.Python3

passed SlapOS.Eggs.UnitTest-Master.Python3

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passed SlapOS.Eggs.UnitTest-Master.Python3

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failed SlapOS.Eggs.UnitTest-Master.Python3

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