Crop the jetpack_version (sdkVersion) received from harness-options.json (bug 986221)

fix [bug 986221](https://bugzilla.mozilla.org/show_bug.cgi?id=986221)

Allow the upload of new versions of addons developped with the development
version of the SDK (for the upcoming australis).

It was prevented because the ```sdkVersion``` from the
```harness-options.json``` file is too long to fit in the
```Files.jetpack_version``` (max_length=10) field.