Add test for checking the xml output contains required nodes

Author: thk123

regression/cbmc-incr-oneloop/alarm2/test-xml-output.desc

@@ -0,0 +1,10 @@
+CORE
+main.c
+--incremental-loop main.0 --unwind-min 5 --unwind-max 10 --xml-ui
+^EXIT=10$
+^SIGNAL=0$
+<text>VERIFICATION FAILED</text>
+<current-unwinding>1</current-unwinding>
+<refinement-iteration>1</refinement-iteration>
+--
+^warning: ignoring