qemu.tests: Add heavy disk write load test for windows guests

Add heavy disk write load test for windows guests. Using Crystal
Disk Mark [1] to generate the write load inside the guest. And set the
default cache to writeback in this test.

changes from v1:
  - Record steps in INFO logs
  - Close the session after test
  - Add command empty check

[1] Crystal Disk Mark is a BSD licensed program
    http://crystalmark.info/software/CrystalDiskMark/manual-en/License.html

    It can be downloaded here:
    http://crystalmark.info/software/CrystalDiskMark/index-e.html

    The file will be added to the winutils.iso
Signed-off-by: NYiqiao Pu <ypu@redhat.com>
Acked-by: NFeng Yang <fyang@redhat.com>

qemu/tests/cfg/win_disk_write.cfg

+- win_disk_write:
+    virt_test_type = qemu
+    only Windows
+    type = win_disk_write
+    drive_cache = writeback
+    crystal_install_cmd = D:\cystaldisk_install.exe
+    crystal_run_cmd = D:\run_cystalfdisk.exe

qemu/tests/win_disk_write.py

+import logging
+from autotest.client.shared import error
+
+
+@error.context_aware
+def run_win_disk_write(test, params, env):
+    """
+    KVM virtio viostor heavy random write load:
+
+    1) Log into a guest
+    2) Install Crystal Disk Mark [1]
+    3) Start Crystal Disk Mark with heavy write load
+
+    @param test: QEMU test object
+    @param params: Dictionary with the test parameters
+    @param env: Dictionary with test environment.
+    @note: Crystal Disk mark is BSD licensed software
+    http://crystalmark.info/software/CrystalDiskMark/manual-en/License.html
+    @see: http://crystalmark.info/software/CrystalDiskMark/index-e.html
+    """
+    error.context("Try to log into guest.", logging.info)
+    vm = env.get_vm(params["main_vm"])
+    vm.verify_alive()
+    timeout = float(params.get("login_timeout", 240))
+    session = vm.wait_for_login(timeout=timeout)
+
+    crystal_install_cmd = params.get("crystal_install_cmd")
+    crystal_run_cmd = params.get("crystal_run_cmd")
+    test_timeout = float(params.get("test_timeout", "7200"))
+
+    error.context("Install Crystal Disk Mark", logging.info)
+    if crystal_install_cmd:
+        session.cmd(crystal_install_cmd, timeout=test_timeout)
+    else:
+        raise error.TestError("Can not get the crystal disk mark"
+                              " install command.")
+
+    error.context("Start the write load", logging.info)
+    if crystal_run_cmd:
+        session.cmd(crystal_run_cmd, timeout=test_timeout)
+    else:
+        raise error.TestError("Can not get the load start command.")
+
+    session.close()