Summary:
Currently HarnessTest.Randomized is already split but some of the splits are faster than the others. The reason is that each split takes a continuous range of the generated args and the test with later args takes longer to finish. The patch evenly split the args among splits in a round robin fashion.
Before:
```
[ OK ] HarnessTest.Randomized1n2 (2278 ms)
[ OK ] HarnessTest.Randomized3n4 (1095 ms)
[ OK ] HarnessTest.Randomized5 (658 ms)
[ OK ] HarnessTest.Randomized6 (1258 ms)
[ OK ] HarnessTest.Randomized7 (6476 ms)
[ OK ] HarnessTest.Randomized8 (8182 ms)
```
After
```
[ OK ] HarnessTest.Randomized1 (2649 ms)
[ OK ] HarnessTest.Randomized2 (2645 ms)
[ OK ] HarnessTest.Randomized3 (2577 ms)
[ OK ] HarnessTest.Randomized4 (2490 ms)
[ OK ] HarnessTest.Randomized5 (2553 ms)
[ OK ] HarnessTest.Randomized6 (2560 ms)
[ OK ] HarnessTest.Randomized7 (2501 ms)
[ OK ] HarnessTest.Randomized8 (2574 ms)
```
Closes https://github.com/facebook/rocksdb/pull/3808
Differential Revision: D7882663
Pulled By: maysamyabandeh
fbshipit-source-id: 09b749a9684b6d7d65466aa4b00c5334a49e833e
fc522bdb3e