Merge pull request #1202 from Zhengtong/s390x_pxe_check

s390x: add additional params for s390x plaform for pxe_boot testing

generic/tests/cfg/pxe_boot.cfg

@@ -16,6 +16,9 @@
     image_verify_bootable = no
     kill_vm = yes
     kill_vm_gracefully = no
+    s390x:
+        extra_params += " -no-shutdown"
+        bootindex_nic1 = 0
     # pxe_boot does not work for macvtap backend, as pxe can't
     # capture the packet from the macvtap tap port, disable it
     # for macvtap temporarily, will fix it in the furture.