Break test suite into separated gem sets

Since the number of instrumented libraries has grown, the test suite has hit an increasing number of conflicts between libraries.  

The latest issue is that the moped gem requires a newer version of the bson gem and mongo still requires the older gem.  The two versions are incompatible and the newer is not backward compatible.

We should break the test suite into gem sets so that these two libraries are tested separately.  My initial thought is that we should use something like the [appraisal](https://github.com/thoughtbot/appraisal) gem to do this.