Tucked behind a pediatric dental office just off 3300 South is a 20-foot shipping container that Steven Flaco Fernandez has turned into something much bigger than its footprint.It is his barbershop, his growing business and, beginning next month, his full-time career.I just feel so happy with what Im doing now, Fernandez said.The 26-year-olds idea for the unconventional shop reaches back to his childhood in El Salvador, where he remembers gettin…