GetOldestXmin: fix VACUUM during upgrade

There are no distributed transactions during binary upgrade, so we can
ignore them. This is a backport from commit fdab8817 in master.

src/backend/cdb/cdbdistributedsnapshot.c

@@ -69,6 +69,13 @@ localXidSatisfiesAnyDistributedSnapshot(TransactionId localXid)
 	if (!IsUnderPostmaster || !IsNormalProcessingMode())
 		return false;
 
+	/*
+	 * During upgrade, there is no distributed system to query, and no way a
+	 * distributed transaction could be looking at a tuple right now.
+	 */
+	if (IsBinaryUpgrade)
+		return false;
+
 	/*
 	 * If don't have snapshot, can't check the global visibility and hence
 	 * return not to perform clean the tuple.