tests: Add rtc-test (fix test regression)

Commit 93e9eb6808c886f5f1c903b7ced1eed65de2ba39 added fdc-test,
but accidentally removed rtc-test because check-qtest-i386-y was
not enhanced but set twice.

This patch adds rtc-test again (and sorts both tests alphabetically).

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
