Why upgrading RHV-H from 4.0 to 4.2 is failing during migrate_var with error "No such file or directory S57glusterfind-delete-post"

Issue

• Upgrading RHV-H from 4.0 to 4.2 is failing with the error below.

2018-08-10 19:53:18,601 [DEBUG] (migrate_var) Copying /tmp/mnt.6fSmc//var/lib/glusterd/hooks/1/delete/post/S57glusterfind-delete-post to /var/lib/glusterd/hooks/1/delete/post/S57glusterfind-delete-post
2018-08-10 19:53:29,742 [DEBUG] (MainThread) Traceback (most recent call last):
  File "/tmp/tmp.ybG3syJOJ9/usr/lib/python2.7/site-packages/imgbased/utils.py", line 1491, in run
    self._function(*self._args, **self._kwargs)
  File "/tmp/tmp.ybG3syJOJ9/usr/lib/python2.7/site-packages/imgbased/plugins/osupdater.py", line 245, in migrate_var
    shutil.copy2(newlv_path, realpath)
  File "/usr/lib64/python2.7/shutil.py", line 130, in copy2
    copyfile(src, dst)
  File "/usr/lib64/python2.7/shutil.py", line 82, in copyfile
    with open(src, 'rb') as fsrc:
IOError: [Errno 2] No such file or directory: u'/tmp/mnt.6fSmc//var/lib/glusterd/hooks/1/delete/post/S57glusterfind-delete-post'