multiversion suite should use targeted linux builds

Currently, all Linux variants for the multiversion suite use the generic Linux/x86_64 build. The multiversion suite should instead use the targeted edition for each Linux variant, and only use the generic Linux build if a targeted build is not available for that version of MongoDB.

This will more closely test what a customer upgrade scenario. It will have a secondary benefit of reducing the number of platforms we run the gccgo builds of the 3.2 version of mongorestore which fail often due to a gccgo bug.