Shaun McConnon last week stepped down as CEO of Cambridge-based BitSight Technologies Inc., a cybersecurity ratings startup that has raised $95 million and been identified as a potential IPO candidate. Though McConnon will stay on as BitSight's executive chairman, he says his long career as a CEO is over. Though he's never founded his own firm, in the past 20 years McConnon has led three local security companies from the earliest stages through acquisitions of over a hundred million dollars.