Fix issue with scalar/non-scalar lists

Fixes #751, originally reported from:
https://forums.aws.amazon.com/thread.jspa?messageID=534743&#534743

The basic issue was that we were looking at the first element in the
list to determine whether or not we should handle something as a list
or not.  With `--query` you can have a heterogenous list so we need
to check all elements, otherwise you'd get lists such as:

```
foo	[{'Value': 'baz', 'Key': 'bar'}]
foo	[{'Value': 'baz', 'Key': 'bar'}]
```

cc @danielgtaylor