[SYSTEMDS-3893] Fix out-of-core test case (metadata file locations)

The test failure of not finding the mtd-file did not show up in local
tests, because locally we do not clean the test directories, and from
development there were both Xmtd and X.mtd existing.

Author: mboehm7

src/test/java/org/apache/sysds/test/functions/ooc/SumScalarMultiplicationTest.java

@@ -73,7 +73,7 @@ public void testSumScalarMult() {
 			MatrixBlock mb = MatrixBlock.randOperations(rows, cols, 1.0, -1, 1, "uniform", 7);
 			MatrixWriter writer = MatrixWriterFactory.createMatrixWriter(FileFormat.BINARY);
 			writer.writeMatrixToHDFS(mb, input(INPUT_NAME), rows, cols, 1000, rows*cols);
-			HDFSTool.writeMetaDataFile(input(INPUT_NAME+"mtd"), ValueType.FP64, 
+			HDFSTool.writeMetaDataFile(input(INPUT_NAME+".mtd"), ValueType.FP64, 
 				new MatrixCharacteristics(rows,cols,1000,rows*cols), FileFormat.BINARY);
 
 			runTest(true, false, null, -1);