Make sure we discover the major / minor correctly.

* Fixes https://github.com/opscode/chef/issues/2202.

The reason we can't find a 10.10 package is because we can't resolve the minor version correctly. Existing regexps end up dividing the version to be something like this:

```
irb(main):001:0> /^([^\.]*)(\.([^\.]*))*/.match("10.10")
=> #<MatchData "10.10" 1:"10" 2:".10" 3:"10"
```

Due to the `.` in the minor version, we end up making a string comparison instead of an integer comparison [here](https://github.com/opscode/opscode-omnitruck/blob/master/lib/platform_dsl.rb#L85-L105).

Specs are looking :green_apple: with this. However I'm not sure if we can get any input different than `X`, `X.Y`, `X.Y.Z` as version.

/cc: @lamont-granquist, @schisamo