Merge #16293: test: Make test cases separate functions

Summary:
faf8318c55a6001270a6fc8ed2298767099bafba test: Split fundrawtx test into subtests (MarcoFalke)
fa6fba3bc8013d7f813edd71f152d86eab907e4d test: Make local symbols in run_test members (MarcoFalke)

Pull request description:

This prevents scope-leak of symbols that are supposed to be local to one test case.

Top commit has no ACKs.

Backport of Core PR16293

Test Plan: test_runner.py rpc_fundrawtransaction

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D7688