Merge pull request #257 from ypu/serial_modprobe

qemu.tests: Add a case for remove and load virtio-serial driver

qemu/tests/cfg/serial_modprobe.cfg

+- serial_modprobe: install setup image_copy unattended_install.cdrom
+    type = virt_subtest_combine
+    kill_vm_on_error = yes
+    virtio_ports_fixed = "vs1"
+    vrtio_port_type_fixed = "serialport"
+    only Linux
+    login_timeout = 240
+    subtests = check_device remove_mod check_no_mod check_no_device load_mod check_device
+    cmd_check_device = ls /dev/vport0p1
+    cmd_check_no_device = ls /dev/vport0p1; [ `echo $?` != 0 ]
+    cmd_remove_mod = rmmod virtio_console
+    cmd_load_mod = modprobe virtio_console
+    cmd_check_no_mod = lsmod | grep virtio_console; [ `echo $?` != 0 ]
+    subtest_type = guests