CXX-365 Test heap1 storage engine

So, this is an interesting design decision.  You've chosen to have the "Ubuntu1404" machine test across different storage engines, right?  The other choice, and we can talk about which is more intuitive, is to have an "Ubuntu1404 Heap1" buildvariant that is its own separate entity.  On MCI, this would show up as its own build, which is kind of appealing to me.

Also, doing that instead might stop us from having to add as many new tasks/functions.  For example, the "integration test latest" and "integration test latest with heap1" tasks are almost identical, and call almost identical "set version latest (with heap1)" functions underneath.  The only difference that I see is that the "with heap1" version of the function set the "orchestration_preset" expansion.  On a separate buildvariant, we could just set that field, and get rid of "integration test latest with heap1."  We wouldn't need a separate list of storage engine tests, they'd just run the basic tests.

It really depends how we want to treat different storage engines.  If we treat them the way we're choosing to treat different versions of mongod (2.2, 2.4, 2.6) then adding new tasks to existing buildvariants (as you've done here) is probably the better way to do this.  If we treat different storage engines as different logical entities from server versions, then I would advocate for changing the design here, because it keeps our config file from exploding.  Thoughts, @spencerjackson, @TylerBrock, and @acmorrow ?