Compile each test in its own java_test() target so they can run in
parallel, reducing total time spent testing on large machines.
$ buck test --all
[-] PROCESSING BUCK FILES...FINISHED 0.3s [100%]
[-] BUILDING...FINISHED 2.9s [100%] (351/383 JOBS, 351 UPDATED, 0.0% CACHE MISS)
[-] TESTING...FINISHED 98.1s (3360 PASS/15 SKIP/0 FAIL)
Change-Id: I8d6541268315089299f933ed23d785b1b3431133