Pembrolizumab and Capecitabine in Treating Patients With Locally Advanced or Metastatic Triple Negative or Hormone-Refractory Breast Cancer That Cannot Be Removed by Surgery

estrogen receptor negative, her2/neu negative, progesterone receptor negative, recurrent breast carcinoma, stage iii breast cancer, stage iiia breast cancer, stage iiib breast cancer, stage iiic breast cancer, stage iv breast cancer, triple-negative breast carcinoma, interventional, phase2