WIP workflows: Check if record exist in HP

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
Not a big deal, but this variable should perhaps just be inside some config.py or maybe passed as argument to the functions below and be a parameter of the workflow tasks?

We can also predefine the existence of the KB now using the `mixer` sources we have to pre-load DB initial states.

I propose to add to knwKB.json so that it is there from the start:
```
    ,{
        "description": "Contains identifiers of records in Holding Pen",
        "id": 11,
        "kbtype": "w",
        "name": "HP_IDENTIFIERS"
    }
```