Merge #7696: Fix de-serialization bug where AddrMan is left corrupted

1475ecf Fix de-serialization bug where AddrMan is corrupted after exception * CAddrDB modified so that when de-serialization code throws an exception Addrman is reset to a clean state * CAddrDB modified to make unit tests possible * Regression test created to ensure bug is fixed * StartNode modifed to clear adrman if CAddrDB::Read returns an error code. (EthanHeilman)