The image-api's measurement.json includes a setting for warnOnly
that should be followed by default. Enforcing all measurments is
currently not possible as some of them are unstable.
* Merge measurements.image.json and measurements.json into latter.
* Use static (known) measurement values for the ones we cannot precompute.
Signed-off-by: Fabian Kammel <fk@edgeless.systems>
