qemu.tests: add qemu_disk_img_convert tests

Implement to test qemu-img convert function; convert base image or
snapshot image from one format to another format, then check image content
not changed after image convert;

Changes from V1:
    replace params.get() with params[] to avoid missing param errors.
Signed-off-by: NXu Tian <xutian@redhat.com>

qemu/tests/cfg/qemu_disk_img.cfg

+# Notes:
+# For windows guest, you can download md5sum.exe from http://www.brothersoft.com/md5sum-81781.html,
+# then add parents dir to $PATH or config md5sum in share/cfg/guest-os/Windows.cfg;
+- qemu_disk_img:
+    only qcow2
+    virt_test_type = qemu
+    type = qemu_disk_img
+    image_chain= "image1"
+    kill_vm = yes
+    start_vm = no
+    image_size = 20G
+    # md5sum binary path
+    md5sum = "md5sum"
+    force_create_image = no
+    backup_image_before_testing = yes
+    restore_image_before_testing = yes
+    tmp_file_name = /tmp/test.img
+    file_create_cmd = "dd if=/dev/urandom of=%s bs=4k count=250"
+    variants:
+        - convert:
+            type = qemu_disk_img_convert
+            guest_file_name = /tmp/test.img
+            variants:
+                - base_to_qcow2:
+                    image_convert = "image1"
+                    convert_name_image1 = "images/image1_to_qcow2"
+                    convert_format_image1 = "qcow2"
+                - base_to_raw:
+                    image_convert = "image1"
+                    convert_name_image1 = "images/image1_to_raw"
+                    convert_format_image1 = "raw"
+                - snapshot_to_qcow2:
+                    image_convert = "sn1"
+                    image_chain += " sn1"
+                    image_name_sn1 = "images/sn1"
+                    image_format_sn1 = "qcow2"
+                    convert_name_sn1 = "images/sn1_to_qcow2"
+                    convert_format_sn1 = "qcow2"

qemu/tests/qemu_disk_img_convert.py

+import logging
+from autotest.client import utils
+from autotest.client.shared import error
+from virttest import storage
+from qemu.tests import qemu_disk_img
+
+
+class ConvertTest(qemu_disk_img.QemuImgTest):
+
+    def __init__(self, test, params, env):
+        self.tag = params["image_convert"]
+        t_params = params.object_params(self.tag)
+        super(ConvertTest, self).__init__(test, t_params, env, self.tag)
+
+    @error.context_aware
+    def convert(self, t_params={}):
+        """
+        create image file from one format to another format
+        """
+        error.context("convert image file", logging.info)
+        params = self.params.object_params(self.tag)
+        params.update(t_params)
+        cache_mode = params.get("cache_mode")
+        super(ConvertTest, self).convert(params, self.data_dir, cache_mode)
+        params["image_name"] = params["convert_name"]
+        params["image_format"] = params["convert_format"]
+        converted = storage.get_image_filename(params, self.data_dir)
+        utils.run("sync")
+        self.trash.append(converted)
+        return params
+
+def run_qemu_disk_img_convert(test, params, env):
+    """
+    'qemu-img' convert functions test:
+
+    @param test: Qemu test object
+    @param params: Dictionary with the test parameters
+    @param env: Dictionary with test environment.
+    """
+
+    base_image = params.get("images", "image1").split()[0]
+    params.update(
+        {"image_name_%s" % base_image: params["image_name"],
+         "image_format_%s" % base_image: params["image_format"]})
+    t_file = params["guest_file_name"]
+    convert_test = ConvertTest(test, params, env)
+    n_params = convert_test.create_snapshot()
+    convert_test.start_vm(n_params)
+
+    # save file md5sum before conversion
+    ret = convert_test.save_file(t_file)
+    if not ret:
+        raise error.TestError("Fail to save tmp file")
+    convert_test.destroy_vm()
+    n_params = convert_test.convert()
+    convert_test.start_vm(n_params)
+
+    # check md5sum after conversion
+    ret = convert_test.check_file(t_file)
+    if not ret:
+        raise error.TestError("image content changed after convert")
+    convert_test.clean()