The drums were ready. So were the signs, the horns, the purple shirts and the protestors. Enough to fill three school buses, which before the protest at noon dropped off picketers who joined many more arriving on their own. But on Thursday, NBCUniversal and its subcontractor ABM Industries averted a major protest from janitors by rehiring more than 100 that their union claimed had been unjustly laid off at the beginning of the week. And so a demonstration staged by Service Employees International Union-United Service Workers West (SEIU-USWW) at Studio City’s South Weddington Park that originally was intended to shame the major entertainment company became instead a celebration of the deal. Negotiations between NBCU, ABM and the union continued nearly right up until the protest’s noon start time. After pumping the crowd up in the park, with 10 Universal City Plaza looming in the backdrop, union president David Huerta delivered the news to his members in Spanish that the parties had agreed that janitors could be rehired and would receive backpay. “They knew the workers …