Don't return multiple elements for grain 'osmajorrelease'.

Before this fix, the output of the 'osmajorrelease' grain looked like
this:

    osmajorrelease:
        7
        0.1406

Now it'll only return the actual major release number:

    osmajorrelease: 7
Merge pull request #15337 from eliasp/2014.7-grains.osmajorrelease

Don't return multiple elements for grain 'osmajorrelease'.