Corrected values of Earth shape scale factors.

This PR corrects some Earth shape scale factors in GRIB testing data, and is closely tied to SciTools/iris#691.

There is a bug in the way iris interprets some of the GRIB Earth shape scale factors, it uses them as a multiplier when it should use them as a decimal shift. The files use to test this behaviour were constructed with the incorrect interpretation in mind, and incorrectly use scale factors of 1 instead of 0, this PR corrects this.

I have only modified the files that directly use these scale factors, choosing to leave the others as they are since iris should be detecting that the `shapeOfTheEarth` key indicates not to use them anyway.

Confirmation that SciTools/iris#691 is addressing the correct problem might be useful before merging this.