By Ivelisse Rivera, Rich McKay and Scott DiSavino SAN JUAN, Puerto Rico/ATLANTA/NEW YORK (Reuters) -Some 80% of homes and businesses in Puerto Rico still lacked power on Tuesday as rains from Hurricane Fiona receded, leaving residents complaining that the island’s troubled electrical grid was still a mess before the storm, despite billions of dollars in funding to improve it. Power provider LUMA Energy said it had restored service to more than 100,000 customers and crews were still working to bring back power for others. Fiona hit Puerto Rico on Sunday, causing an island-wide outage for its 1….