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