In Trinity Repertory Co.’s latest production, it’s the end of the world and seven survivors of a pandemic are holed up in a building, barricading themselves against contagion and whatever else may be lurking outside. Described as “horrifying, hilarious and incredibly, eerily true,” “Social Creatures” was written specifically for Trinity Rep and opens in previews on Friday. The play was created by Jackie Sibblies Drury, a new playwright and graduate of the Brown MFA playwriting program.