The University of Delaware student busted with a huge cache of guns , body armor and a notebook filled with alleged plans to shoot up his school is an Afghan national who spent time as a refugee in Pakistan before immigrating to the US, officials told The Post. Luqmaan Khan, 25, was born in Afghanistan, then fled at some point to Pakistan where he lived as a refugee for “a few years,” the Pakistani embassy told The Post. He then came to the US, where he became a citizen. US officials first