In the middle of a worship song on Sunday, the morning after Cuba’s electrical grid collapsed for a second time in six days, the preacher at Renewal in Christ Church in Havana said he had a message to share that came to him in a dream.  Sunlight splashed in through an open window to the right of the raised platform where he stood, as a battery-powered light affixed to the ceiling shone weakly over the pulpit. A row of desk fans, plugs dangling, lined the top of the concrete walls of the shadowed sanctuary.  Cuba suffers 3rd countrywide blackout this month amid U.S.…