e: small fixes to port of e_fm udisk to edbus
- no need for calling edbus_message_error_get() if we are not getting the error message
- rename confusing vars:
- A dict is this complete type: "a{sv}", i.e. an array with key-values pairs (though the value could very well be 's', or 'u' or another basic type)
- An entry (or dict_entry, or de) is *the* key-value pair.
- Use eina_stringshare_replace when possible