aws cloudformation multiple --parameters flags

It should be possible to

```
aws cloudformation create-stack --parameters file://p.json --parameters "ParameterKey=AdditionaParam,ParameterValue=some_value"
```

Such that one can provide parameters from both a file and in line. It seems that is not possible now, but sadly the command does not exit with an error stating so. Either add the feature or make an error handler.