slapos_panel: Get monitor-setup-url from '_' parameter

   Whenever the serialization is JSON-in-xml the parameters are uploaded into {'_' : '{}') format.
2 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:36:44

failed SlapOS.Eggs.UnitTest-Master.Python3

00:30:26