qemuhelptest: Add new qemuCap flag

Latest patch a1a83c58 introduces new qemu capability flag
QEMU_CAPS_FSDEV_READONLY. However, it was missing in qemuhelptest
making test for qemu-1.0 fail.

tests/qemuhelptest.c

@@ -647,7 +647,8 @@ mymain(void)
             QEMU_CAPS_NO_SHUTDOWN,
             QEMU_CAPS_PCI_ROMBAR,
             QEMU_CAPS_ICH9_AHCI,
-            QEMU_CAPS_NO_ACPI);
+            QEMU_CAPS_NO_ACPI,
+            QEMU_CAPS_FSDEV_READONLY);
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }