slapos/cli: Nicer error messages for cachelookup binary-sr

Status Job ID Name Coverage
  External
failed SlapOS.Eggs.UnitTest-Paul.Slapos.Core.Tests.Python2

00:33:51

failed SlapOS.Eggs.UnitTest-Paul.Slapos.Core.Tests.Python3

00:30:00

failed SlapOS.Eggs.UnitTest-Paul.Slapos.Core.Tests.Python2

00:22:52

failed SlapOS.Eggs.UnitTest-Paul.Slapos.Core.Tests.Python3

00:22:59