NIFI-5949: Addressed problematic error handling logic in PutKudu. Als…

[markap14]

…o removed AbstractKudu and moved all logic into PutKudu, as the abstract class was clearly designed to be extended only by PutKudu and no other processors exist for Kudu

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[markap14]

@jtstorck any chance you can take a look at this and make sure that I didn't break anything? :)

[jtstorck]

Reviewing...

[jtstorck]

Tested the PutKudu changes, looking good. Needed to add an explicit .toString() call on rowErrors to avoid an issue with an IllegalStateException getting thrown when iterating through rowErrors to log them.