Update NiPyAPI to be roughly forward compatible with NiFi-2.x line.

[Chaffelson]

Updates NiPyAPI to be roughly forward compatible with NiFi-2.x line.
Note that this does not implement the full API Clients for NiFi-2.x and NiFi-Registry-2.x, it only ensures that calls made using this client generated from the 1.27.0 swagger definition appear to work correctly according to existing tests.

• Instruct pytest to not report insecure http requests to localhost for docker testing
• Templates are deprecated in nifi-2x, remove from tests for newer versions
• Add function to check registry version using newer aboutapi() call
• Update utils.check_version to ignore any non-semver elements of a version string and use newer registry version api call if available
• Update registry client creation to handle nifi-2x structure
• Update Testing to treat NiFI-2.x as latest
• Deprecate very old nifi-1x versions from regression testing
• Fix get processor test to use a processor available in all nifi versions, GenerateFlowfile

[ottobackwards]

A couple of high level thoughts here. According to nifi, the 1.x line and the 2.x line are concurrent release paths. I'm not sure just having a "latest" and having it be 2.x-M is right here, as I don't know when the end of 1.x will be.

Also, It isn't clear to me, and it isn't in the readme, what the clear status of 2x is, or rather what the answer is to "Is this the official 2.x support release?".

I think the disposition wrt 2.x and the expectations or limitations need to be stated.
thoughts?

[Chaffelson]

A couple of high level thoughts here. According to nifi, the 1.x line and the 2.x line are concurrent release paths. I'm not sure just having a "latest" and having it be 2.x-M is right here, as I don't know when the end of 1.x will be.

yeah good point. Latest was just a convenience inherited from typical docker notation.
Perhaps it would be best to keep the 1.x line as the 'latest' for now, but put in the 2.0.0-Mx line as tested alternates? That's an easy modification.

Also, It isn't clear to me, and it isn't in the readme, what the clear status of 2x is, or rather what the answer is to "Is this the official 2.x support release?".

NiFi-2.x has moved to OpenAPI-3.0.1 as the API definition standard, which is going to require a major rewrite.
I think probably what needs to happen is that split into a 1.x maint branch that keeps the Swagger-2.0 base clients derived from the NiFi-1.x line going, and start up a 2.x branch for moving to OpenAPI3.

Thus far I've managed to keep both backwards Py2 compatibility and forwards NiFi-2.x compatibility, but it's getting very difficult these days.

I suspect we'll be moving to a 1.x release of NiPyAPI which is python3 only along with moving to OpenAPI 3.0.1 based clients from NiFi-2.x as it seems an obvious point to cut over.

So for this 0.21.0 release, we do not officially support NiFi-2.x, but it seems to work and tickets opened for support will be investigated - does that sound good?

[Chaffelson]

@ottobackwards updated the readme and docker test files as noted.