Update feeRate (BTC/kvB) to fee_rate (sat/vB) in wallet_bumpfee

as the feeRate argument should soon be deprecated.

Also loosen one test (and a similar one) that caused a one-off CI failure with:
expected message
'Insufficient total fee 0.00000141, must be at least 0.00001704 (oldFee 0.00000999 + incrementalFee 0.00000705)'
actual message
'Insufficient total fee 0.00000141, must be at least 0.00001712 (oldFee 0.00001007 + incrementalFee 0.00000705)'

test/functional/wallet_bumpfee.py

@@ -107,12 +107,10 @@ class BumpFeeTest(BitcoinTestFramework):
             assert_raises_rpc_error(-3, "Unexpected key {}".format(key), rbf_node.bumpfee, rbfid, {key: NORMAL})
 
         # Bumping to just above minrelay should fail to increase the total fee enough.
-        assert_raises_rpc_error(-8, "Insufficient total fee 0.00000141, must be at least 0.00001704 (oldFee 0.00000999 + incrementalFee 0.00000705)",
-            rbf_node.bumpfee, rbfid, {"fee_rate": INSUFFICIENT})
+        assert_raises_rpc_error(-8, "Insufficient total fee 0.00000141", rbf_node.bumpfee, rbfid, {"fee_rate": INSUFFICIENT})
 
         self.log.info("Test invalid fee rate settings")
-        assert_raises_rpc_error(-8, "Insufficient total fee 0.00, must be at least 0.00001704 (oldFee 0.00000999 + incrementalFee 0.00000705)",
-            rbf_node.bumpfee, rbfid, {"fee_rate": 0})
+        assert_raises_rpc_error(-8, "Insufficient total fee 0.00", rbf_node.bumpfee, rbfid, {"fee_rate": 0})
         assert_raises_rpc_error(-4, "Specified or calculated fee 0.141 is too high (cannot be higher than -maxtxfee 0.10",
             rbf_node.bumpfee, rbfid, {"fee_rate": TOO_HIGH})
         assert_raises_rpc_error(-3, "Amount out of range", rbf_node.bumpfee, rbfid, {"fee_rate": -1})
@@ -421,7 +419,7 @@ def test_watchonly_psbt(self, peer_node, rbf_node, dest_address):
     self.sync_all()
 
     # Create single-input PSBT for transaction to be bumped
-    psbt = watcher.walletcreatefundedpsbt([], {dest_address: 0.0005}, 0, {"feeRate": 0.00001}, True)['psbt']
+    psbt = watcher.walletcreatefundedpsbt([], {dest_address: 0.0005}, 0, {"fee_rate": 1}, True)['psbt']
     psbt_signed = signer.walletprocesspsbt(psbt=psbt, sign=True, sighashtype="ALL", bip32derivs=True)
     psbt_final = watcher.finalizepsbt(psbt_signed["psbt"])
     original_txid = watcher.sendrawtransaction(psbt_final["hex"])