tests: Print XML file name in verbose CPU test

It's not totally obvious that a failure in

    CPU guest data(x86): host/guest (models, pref="qemu64")

test means one needs to fix

    x86-host+guest,models,qemu64-result.xml

where the expected XML is stored. Better to provide a nice hint in
verbose mode for failed tests.

tests/cputest.c

@@ -180,6 +180,8 @@ cpuTestCompareXML(const char *arch,
         goto cleanup;
 
     if (STRNEQ(expected, actual)) {
+        if (virTestGetVerbose())
+            fprintf(stderr, "\nCompared to %s-%s.xml", arch, name);
         virtTestDifference(stderr, expected, actual);
         goto cleanup;
     }