PCT-686: pfs status checking

This block was confusing, unclear.  Then it struck me as familiar and I remembered: https://github.com/percona/percona-agent/blob/release/qan/worker.go#L203

Problem is: the original code ^ is wrong.  Despite the code comment (which this code lacks), it's not really sorting anything.  Sorting happens here https://github.com/percona/percona-agent/blob/release/qan/report.go#L51.