moved the perf logging stuff into a class in h2o_perf.py so h2o.py isn't cluttered, and easier to modify/add and save some state.
only used if build_cloud gets enable_benchmark_log=True and parse is enabled to log with benchmarkLogging=True. benchmark log is current dir as benchmark_<testname>.log. appends to existing file.
Merge branch 'master' of github.com:0xdata/h2o