Tests/library for 'update task' endpoint

[gshif]

• Helper function for update task endpoint.
• Define tests for update task endpoint.
• Implement tasks for update task endpoint.

[gshif]

• Implemented update_task function that takes task_id, name, flux, token, status, cron, every, offset parameters and returns dictionary of values in response object

[gshif]

• [x] Update one of the fields in the request body.
  • [x] status
    • from active to inactive
    • from inactive to active
    • from either active/inactive to unsupported status
  • [x] flux
  • [x] name (in the flux script)
    • from existing name to a different name.
    • from existing name to an empty name.
    • from existing name to a very long name.
    • from existing name to a single character name.
  • [x] every (when flux has crone and every)
  • [x] cron (when flux has cron and every)
  • [x] offset (add/remove)
  • [x] token (valid/invalid)
• [x] Update with cron and every in the same request body (should not be possible, either cron or every)
• [x] Update with not supported status (neither active nor inactive)
• [ ] Update with illegal flux script.
• [x] Update with not supported time format in every and offset fields.
• [x] Update with not supported cron format.
• [ ] Update multiple fields. (tests can be parameterized)

[kevinhogan111]

these tests have been running under test_gateway_update_tasks.py for quite awhile, closing this.