Make the test less specific.

Remove the need to add every benchmark to the list of all benchmarks.

Also, add some hard-coding of the location of the benchmark executable.
Add a test to make sure the benchmark exists so it's possible to detect
if the executable changes location.

Finally, make the tests isolated so that they finish in half the time.

Test: Ran unit tests.
Change-Id: I1e59eb283e31d29b14e54c44ac865827c9704127