Implement Slapos UI test: Invoice test

See merge request !236
4 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS.Eggs.UnitTest-Master.Python2

00:09:45

failed SlapOS.Eggs.UnitTest-Master.Python3

00:07:20

failed SlapOS.Eggs.UnitTest-Master.Python2

00:18:14

failed SlapOS.Eggs.UnitTest-Master.Python3

00:15:25