Merge #11771: [tests] Change invalidtxrequest to use BitcoinTestFramework

Summary:
PR11771 backport https://github.com/bitcoin/bitcoin/pull/11771/files
95e2e9a [tests] Change invalidtxrequest to use BitcoinTestFramework (John Newbery)
359d067 [tests] Fix flake8 warnings in invalidtxrequest (John Newbery)
c32cf9f [tests] Add P2PDataStore class (John Newbery)
cc046f6 [tests] Reduce NodeConn connection logging from info to debug (John Newbery)

Pull request description:

Next step in #10603

- first commit changes log level for an internal log from INFO to DEBUG. (Not really related, but I started finding the INFO level logging annoying when debuging test failures)
- second commit introduces a `P2PStub` class - a subclass of `NodeConnCB` which has its own block and tx store and responds appropriately to getdata requests. Not all the functionality is used in `invalidtxrequest.py`, but will be used in `invalidblockrequest.py` and `p2p-fullblocktest` when those are changed to use `BitcoinTestFramework`
- third commit tidies up `invalidtxrequest.py`
- fourth commit removes usage of `ComparisonTestFramework`

Backport note: the "Invalid OP_IF construction" was changed to a pushonly failure.

Depends on D3501

Test Plan: test_runner.py

Reviewers: deadalnix, jasonbcox, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Maniphest Tasks: T669

Differential Revision: https://reviews.bitcoinabc.org/D3494