(QENG-807) add --collect-perf-data option, rspec tests, and yard docs

If beaker is run with "--collect-perf-data" it will ensure sysstat is installed and configured on the Linux hosts before testing begins. After testing is finished, a sar report is sent to logging for each Linux host.
This will also only be called when you have multiple hosts, not if you say, have one host you're profiling, is that behavior you want? I would expect it to add systat to the host packages regardless of how many hosts there were.