Add wallet acceptance / mempool acceptance tests for non-standard variants

Summary:
We want to make sure that everything that is considered 'spendable' by
the wallet will not cause the generation of a nonstandard transaction when
the wallet tries to actually spend it.

Test Plan:

./test_runner.py abc-wallet-nonminpush

Reviewers: deadalnix, jasonbcox, Fabien, #bitcoin_abc

Reviewed By: jasonbcox, Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3880