LOS ANGELES — Teachers picketed and rallied Friday as a strike against the giant Los Angeles Unified School District extended to a fifth day with a new round of contract negotiations underway. Drums, whistles, shouts and honks from supportive drivers echoed through downtown as groups of teachers and backers walked to a rally that drew thousands to Grand Park near City Hall. Negotiations between United Teachers Los Angeles and the Los Angeles Unified School District resumed Friday and continued into the night. “Too many students are missing out on the education they should be getting,” district Superintendent Austin Beutner said.