'It waits for import snapshot to be completed
:param import_task_id: Import task Id for the
current Import Snapshot Task
:type import_task_id: ``str``
:param timeout: Timeout value for snapshot generation
:type timeout: ``float``
:param interval: Time interval for repetative describe
import snapshot tasks requests
:type interval: ``float``
:rtype: :class:``VolumeSnapshot``'

def _wait_for_import_snapshot_completion(self, import_task_id, timeout=1800, interval=15):

    start_time = time.time()
    snapshotId = None
    while (snapshotId is None):
        if ((time.time() - start_time) >= timeout):
            raise Exception(('Timeout    while    waiting    for    import    task    Id    %s' % import_task_id))
        res = self.ex_describe_import_snapshot_tasks(import_task_id)
        snapshotId = res.snapshotId
        if (snapshotId is None):
            time.sleep(interval)
    volumeSnapshot = VolumeSnapshot(snapshotId, driver=self)
    return volumeSnapshot
