Switch evergreen.yml to use task tags for specifying which tests to run on which variant.

This will involve some investigation to determine a good way of selecting which tags to use and then switching etc/evergreen.yml to use those tags.

As a MongoDB engineer,
I want to be able to specify the build variants a task run on via tasks,
so that I don't have to manually add a task to all buildvariants it should run on.

AC: The tasks run of each build variant should not change.