Add rng driver load test

1. repeat load/unload 10 times
2. unload during random read
Signed-off-by: NSuqin Huang <shuang@redhat.com>

qemu/tests/cfg/rng_driver_load.cfg

+- rng_driver_load:
+    only Linux
+    no no_virtio_rng
+    start_vm = yes
+    login_timeout = 240
+    image_snapshot = yes
+    variants:
+        - load_in_loop:
+            type = driver_load
+            driver_id_pattern = virtio_rng
+            driver_id_cmd = lsmod | grep virtio_rng
+            driver_unload_cmd = modprobe -r virtio_rng
+            driver_load_cmd = modprobe virtio_rng
+            repeats = 10
+        - driver_in_use:
+            type = rng_driver_negative
+            driver_unload_cmd = modprobe -r virtio_rng
+            read_rng_cmd  = "dd if=/dev/random of=/dev/null & echo $!"

qemu/tests/rng_driver_negative.py

+import logging
+import aexpect
+
+from virttest import error_context
+from avocado.core import exceptions
+
+
+@error_context.context_aware
+def run(test, params, env):
+    """
+    KVM driver load test:
+    1) Log into a guest
+    2) Read from virtio-rng device
+    3) Unload the device driver
+    4) Check no crash
+    5) Load the device driver
+
+    :param test: QEMU test object
+    :param params: Dictionary with the test parameters
+    :param env: Dictionary with test environment.
+    """
+    vm = env.get_vm(params["main_vm"])
+    vm.verify_alive()
+    login_timeout = int(params.get("login_timeout", 360))
+    session = vm.wait_for_login(timeout=login_timeout)
+
+    driver_unload_cmd = params["driver_unload_cmd"]
+
+    error_context.context("Read virtio-rng device in background",
+                          logging.info)
+    read_rng_cmd = params["read_rng_cmd"]
+    pid = session.cmd_output(read_rng_cmd)
+    pid = pid.split("\n")[1]
+    logging.info("Check if random read process exist")
+    status = session.cmd_status("ps -p %s" % pid)
+    if status != 0:
+        raise exceptions.TestFail("random read is not running background")
+
+    error_context.context("Unload the driver during random read",
+                          logging.info)
+    try:
+        session.cmd(driver_unload_cmd)
+    except aexpect.ShellTimeoutError:
+        pass
+    error_context.context("Check if there is call trace in guest",
+                          logging.info)
+    try:
+        vm.verify_kernel_crash()
+    finally:
+        try:
+            session.cmd("kill -9 %s" % pid)
+            session.close()
+        except Exception:
+            pass