The hosting service unit tests file was getting pretty big and
unmaintainable. Before the tree diverges too much between 2.5 and 2.6,
and before students get to work on this code, we need to split this up,
which is what this change does.

Each file tests one hosting service or one aspect of the hosting service
app. It'll also be easier to handle merging of code between branches
without worrying about complex conflicts.

Unit tests pass.