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.
An example would be:
```java
@Test public void bluetoothSomething() {
  assumeThat(device.hasBluetooth());
  assertTrue(somethingWithBluetooth());
}
```
You would get an assumption failure when the test was run on a device without bluetooth so the test isn't relevant for that device.