[SPARK-15736][CORE][branch-1.6] Gracefully handle loss of DiskStore files#13479

JoshRosen wants to merge 3 commits intoapache:branch-1.6apache/spark:branch-1.6from

JoshRosen:handle-missing-cache-files-branch-1.6JoshRosen/spark:handle-missing-cache-files-branch-1.6Copy head branch name to clipboard