Summary:
Add a helper class for creating an EdenServer in a unit test.
Most of our existing unit tests only create EdenMount objects, without a full
EdenServer. This new class will make it easier to write tests for
functionality that does require a full EdenServer object.
Reviewed By: chadaustin
Differential Revision: D15492166
fbshipit-source-id: f8b1ce3b78a1160a5d55d305e6bf4b5305cca509