Fixing ELB unit tests.  Also did some PEP8 cleanup on ELB code.

Since we only support Python 3.3 and newer we don't need to use `six.b` and can instead use byte literals or encode strings to bytes:

```python
ATTRIBUTE_SET_RESPONSE = b'some bytes'

### or ###

mock_response.read.return_value = ATTRIBUTE_SET_RESPONSE.encode('utf-8')
```

I think other modules are using literal byte strings for this.