Fix: url not set in json output
  - jenkinsapi.Job instance is false if it has no builds (__len__ method) WTF!
Json improvement: node_id should restart from 0 if there are multiple flows in a single invocation
Fix jobload:
 - poll() is required to make the job immediately available
    - improved mock to enable more testing of jobload
    - improved test
Print error message at the end if fail
Json tests