Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1654347

Description of problem:
Foreman may create duplicate CreateRssNotifications, CreatePulpDiskSpaceNotifications or SendExpireSoonNotifications when restart foreman-tasks.

1. su - postgres c "psql -d foreman -c 'select label,count(label),state from foreman_tasks_tasks where state <> '\''stopped'\'' group by label,state;'"
   label | count | state
   ---------------------------------------------------------
   CreateRssNotifications | 2 | scheduled
   CreatePulpDiskSpaceNotifications | 1 | scheduled
   SendExpireSoonNotifications | 1 | scheduled

The "spawn_if_missing" function is looking for task that is in "scheduled" state during the dynflow startup. If no "CreateRssNotifications" is in "schdeduled" state, then create one. I suspect that the task was not in "scheduled" state previously before Dynflow got terminated and cause Dynflow to create a duplicate task during startup.

/usr/share/foreman/app/jobs/application_job.rb

def self.spawn_if_missing(world)
    return if (Foreman.in_rake? && !Foreman.in_rake?('dynflow:executor')) || Rails.env.test?

pending_jobs = world.persistence.find_execution_plans(filters: { :state => 'scheduled' })
    scheduled_job = pending_jobs.select do |job|
      delayed_plan = world.persistence.load_delayed_plan job.id
      next unless delayed_plan.present?
      arg = delayed_plan.to_hash[:serialized_args].first
      arg.is_a?(Hash) && arg['job_class'] == self.to_s
    end

1. Schedule the job only if it doesn't exit yet
   self.perform_later if scheduled_job.blank?
   end