qemu.tests: add qemu_disk_img_commit test

Implement new test to check qemu-img commit function;

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

@@ -36,3 +36,10 @@
                     image_format_sn1 = "qcow2"
                     convert_name_sn1 = "images/sn1_to_qcow2"
                     convert_format_sn1 = "qcow2"
+        - commit:
+            type = qemu_disk_img_commit
+            guest_file_name = /tmp/test.img
+            image_commit = "sn1"
+            image_chain += " sn1"
+            image_name_sn1 = "images/sn1"
+            image_format_sn1 = "qcow2"

qemu/tests/qemu_disk_img_commit.py

+import logging
+from autotest.client.shared import error
+from qemu.tests import qemu_disk_img
+
+
+class CommitTest(qemu_disk_img.QemuImgTest):
+
+    def __init__(self, test, params, env):
+        self.tag = params.get("image_commit", "image1")
+        t_params = params.object_params(self.tag)
+        super(CommitTest, self).__init__(test, t_params, env, self.tag)
+
+    @error.context_aware
+    def commit(self, t_params={}):
+        """
+        commit snapshot to backing file;
+        """
+        error.context("commit snapshot to backingfile", logging.info)
+        params = self.params.object_params(self.tag)
+        params.update(t_params)
+        cache_mode = params.get("cache_mode")
+        return super(CommitTest, self).commit(params, cache_mode)
+
+def run_qemu_disk_img_commit(test, params, env):
+    """
+    'qemu-img' commit 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"]
+    commit_test = CommitTest(test, params, env)
+    n_params = commit_test.create_snapshot()
+    commit_test.start_vm(n_params)
+
+    # save file md5sum before commit
+    ret = commit_test.save_file(t_file)
+    if not ret:
+        raise error.TestError("Fail to save tmp file")
+    commit_test.destroy_vm()
+    commit_test.commit()
+    commit_test.start_vm(params)
+
+    # check md5sum after commit
+    ret = commit_test.check_file(t_file)
+    if not ret:
+        raise error.TestError("image content changed after commit")
+    commit_test.clean()