Adapt rubygem-mongo to the new name schema

Use the new schema for rubygem in SLE12 and openSUSE 13.2.

>> Btw, the two lines look the same, so what about doing if (SLE>=12) or (openSUSE>=13.2) instead?
>
>A Python behaviour, I think.  I try to avoid long lines.  Also I feel that is more explicit. I will change it

You can just do:
```
platform = node["platform"]
version = node["platform_version"].to_f
if (platform == "suse" && version >= 12) or
   (platform == "opensuse" && version >= 13.2)
  ...
end
```

(which is how I'd do it in python, btw)