SQUASHME: Fix rpc tests that assumed fallback to minRelayTxFee
SQUASHME: Fix rpc tests that assumed fallback to minRelayTxFee

Note from cherry-picker: Skipped changes in mempool_limit

dagurval/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt,dagurval/bitcoinxt,dagurval/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt,bitcoinxt/bitcoinxt,dagurval/bitcoinxt