qemu.tests.cfg: Disable s3/s4 related cases in sr_iov.cfg

Disable s3/s4 related cases on Host_RHEL.6, cause not support
s3/s4 on RHEL6 host.
Signed-off-by: NShuping Cui <scui@redhat.com>

qemu/tests/cfg/sr_iov.cfg

@@ -57,6 +57,7 @@
             repeat_times = 500
             test_timeout = 10000
         - vf_guest_suspend:
+            no Host_RHEL.6
             variants:
                 - vf_assigned:
                     type = guest_suspend