[tests] Small fixups before deprecating generate

In advance of deprecating the generate RPC method, make some small
changes to a small number of inidividual test cases:

- make memory checking less prescriptive in wallet_basic.py
- replace calls to generate with generatetoaddress in wallet_keypool.py
- replace calls to generate with generatetoaddress and fixup label
  issues in wallet_labels.py
- replace calls to generate with generatetoaddress in wallet_multiwallet.py

test/functional/wallet_keypool.py

@@ -73,11 +73,10 @@ class KeyPoolTest(BitcoinTestFramework):
         time.sleep(1.1)
         assert_equal(nodes[0].getwalletinfo()["unlocked_until"], 0)
 
-        # drain them by mining
-        nodes[0].generate(1)
-        nodes[0].generate(1)
-        nodes[0].generate(1)
-        assert_raises_rpc_error(-12, "Keypool ran out", nodes[0].generate, 1)
+        # drain the keypool
+        for _ in range(3):
+            nodes[0].getnewaddress()
+        assert_raises_rpc_error(-12, "Keypool ran out", nodes[0].getnewaddress)
 
         nodes[0].walletpassphrase('test', 100)
         nodes[0].keypoolrefill(100)