Added utility in disk library help to Set io scheduler to a device

Added utility in disk library help to Set io scheduler to a device

Signed-off-by: Praveen K Pandey <praveen@linux.vnet.ibm.com>

avocado/utils/disk.py

@@ -478,3 +478,15 @@ def __sched_path(device_name):
     file_path = f'/sys/block/{device_name}/queue/scheduler'
     return file_path
 
+
+def set_io_scheduler(device_name, name):
+    """
+    Set io scheduler to a device
+    :param device_name:  Device  name example like sda
+    :param name: io scheduler name
+    """
+    if name not in get_io_scheduler_list(device_name):
+        raise DiskError(f"No such IO scheduler: {name}")
+
+    with open(__sched_path(device_name), "w", encoding="utf-8") as fp:
+        fp.write(name)