Added 'make bench' make target to run benchmark tests under 'src/'.

- The 'benchmark' tests are the GTEST test cases or tests with the name containing 'BENCHMARK_'.
- The tests can be inovked by 'make bench' command or 'make check' with a non-zero environment variable MESOS_RUN_BENCHMARKS value.

Review: https://reviews.apache.org/r/20017