Adapt rubygem-mongo to the new name schema

Use the new schema for rubygem in SLE12 and openSUSE 13.2.
> Oh, openSUSE is recognized as a different platform now?
I grep some code in another barclamp that make this distiction using the same ID ('opensuse').  If I understand correctly @tboerger, this is possible in Chef 11.  But I will recheck.

> 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