Write a multiversion test which upgrades through several versions

Although we have tests in various release branches for upgrades from one version to the next, we do not have a test which ensures that we can upgrade through several versions (e.g. 2.6=>3.0=>3.2=>3.4). We should write a test with the following structure:

• For each version downloaded during the multiversion suite setup:
  • Start a node of that version, without clearing data files from the previous iteration.
  • Create a new collection.
  • Insert a document into the new collection.
  • Create an index on the new collection.

We may also want a similar test which does repeated rolling upgrades of a replica set from one version to the next.