slapos_slap_tool: decode before add to lxml.etree

See merge request !606
3 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS-Master.UnitTest-Master

02:21:53

failed SlapOS.Eggs.UnitTest-Master.Python2

00:17:40

passed SlapOS.Eggs.UnitTest-Master.Python3

00:16:01