RDAImage.materialize errors with `colorModel == null`

[drwelby]

Running materialize() on an image object can result in this error:

{'internalJobId': '51ae11a0-60b3-4cef-94dd-aef33007b06c',
 'jobStatus': 'processing',
 'startTime': 1570741069075,
 'endTime': 1570741697202,
 'elapsedTime': 628127,
 'statusMessage': '50070965-218a-4802-a231-a102a4264abf; 1; java.util.concurrent.ExecutionException: java.lang.IllegalArgumentException: colorModel == null!\n44e592c9-0882-448a-98fc-66b6def312a8; 1; java.util.concurrent.ExecutionException: java.lang.IllegalArgumentException: colorModel == null!'}

This is because the defaults set out_format='TILE_STREAM' and TILE_STREAM is only a POC and can not render all graphs.

The correct value should always be out_format='TIF'. Passing this kwarg should fix the error.

In the future this kwarg should be removed and the format hardcoded to TIF.