Improve test coverage of dist processing code

This change adds some additional tests to cover the different
combinations of setting OutputFile and DistFiles properties in the
AndroidMkEntry.

These tests will prevent follow up changes from inadvertently changing
the behavior that some modules rely on.

Test: m nothing
Bug: 174226317
Change-Id: I6ab6f2711a5fa416ea2b84a1e0b8754d525d7a0c