virsystemdtest: Call at least one virSystemdCreateMachine with 'maxthreads' > 0

There was a bug in the code adding TasksMax property. It remained
undetected because all tests used '0' for @maxthreads.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

tests/virsystemdtest.c

@@ -313,7 +313,7 @@ static int testCreateNetwork(const void *opaque G_GNUC_UNUSED)
                                 123,
                                 true,
                                 nnicindexes, nicindexes,
-                                "highpriority.slice", 0) < 0) {
+                                "highpriority.slice", 2) < 0) {
         fprintf(stderr, "%s", "Failed to create LXC machine\n");
         return -1;
     }