Add initial tests for server

[Edmond Cotterell]

Start with probeScheduler

TODO:

• --test mode should use in:memory db for test
• Test that ScheduleProbes:
  • Loads crons for probes where users have their probe_settings set to active
  • Loads crons for probe followups i.e. ENQUEUE_FOLLOWUP_PROBES_HANDLER
• Test that the probes are executed when they are suppose to be ?
  • Perhaps this should not be a probeScheduler test, but a wokerPool test ?