Adapt to latest ddmlib version

This change is a quick adaptation to changes in DDM lib used by Android Gradle plugin 0.14.x.
Closes #208.

That said, I do not have a strong leg to stand on what assumption failure really means. However, it seems to correspond to `error` in previous versions.
I didn't add ignored test handling since it requires additional changes in reports code.

I tested this with combination of spoon gradle plugin and Android plugin 0.14.1.
I see. Well, actually for more than 2 years :)
Do you think this quick change can be accepted (currently ignoring assumption failures just like ignored tests)?
Another question is what has happened with what was called errors previously? Are they all failures now?