Consistently use FormatStateMessage in RPC error output

This will include the error code and debug output as well as the reason string.

See #11955 for the motivation.

test/functional/feature_nulldummy.py

@@ -21,7 +21,7 @@ from test_framework.script import CScript
 from io import BytesIO
 import time
 
-NULLDUMMY_ERROR = "64: non-mandatory-script-verify-flag (Dummy CHECKMULTISIG argument must be zero)"
+NULLDUMMY_ERROR = "non-mandatory-script-verify-flag (Dummy CHECKMULTISIG argument must be zero) (code 64)"
 
 def trueDummy(tx):
     scriptSig = CScript(tx.vin[0].scriptSig)

test/functional/mempool_limit.py

@@ -58,7 +58,7 @@ class MempoolLimitTest(BitcoinTestFramework):
         # specifically fund this tx with a fee < mempoolminfee, >= than minrelaytxfee
         txF = self.nodes[0].fundrawtransaction(tx, {'feeRate': relayfee})
         txFS = self.nodes[0].signrawtransaction(txF['hex'])
-        assert_raises_rpc_error(-26, "66: mempool min fee not met", self.nodes[0].sendrawtransaction, txFS['hex'])
+        assert_raises_rpc_error(-26, "mempool min fee not met, 166 < 411 (code 66)", self.nodes[0].sendrawtransaction, txFS['hex'])
 
 if __name__ == '__main__':
     MempoolLimitTest().main()

test/functional/mining_prioritisetransaction.py

@@ -120,7 +120,7 @@ class PrioritiseTransactionTest(BitcoinTestFramework):
         tx_id = self.nodes[0].decoderawtransaction(tx_hex)["txid"]
 
         # This will raise an exception due to min relay fee not being met
-        assert_raises_rpc_error(-26, "66: min relay fee not met", self.nodes[0].sendrawtransaction, tx_hex)
+        assert_raises_rpc_error(-26, "min relay fee not met (code 66)", self.nodes[0].sendrawtransaction, tx_hex)
         assert(tx_id not in self.nodes[0].getrawmempool())
 
         # This is a less than 1000-byte transaction, so just set the fee