Reorganize the test_apps directory and the binary files it generates

[sgpearse]

With #2878, we will have three directories that hold binaries in our build directory:

• bin
• test_binaries
• debug_binaries

We will also have a legacy directory called test_apps. The binaries in test_apps should be migrated into the aforementioned binary directories. We should consider moving the source files in the root-level test_apps directory into our apps directory.