(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.
I have tested this code and it works with only a single host in the configuration file. In this scenario, it looks like validate_host is called with an array of hosts with only a single element.