Why hosted engine upgrade from 3.6 to 4.0 is failing with permission denied error while injecting the engine backup file

Issue

• Hosted engine upgrade from 3.6 to 4.0 using hosted-engine --upgrade-appliance is failing with Permission denied error.

2017-06-29 14:59:28 DEBUG otopi.context context._executeMethod:142 method exception
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/otopi/context.py", line 132, in _executeMethod
    method['method']()
  File "/usr/share/ovirt-hosted-engine-setup/scripts/../plugins/gr-he-common/vm/boot_disk.py", line 716, in _misc
    ohostedcons.Upgrade.BACKUP_FILE
  File "/usr/lib/python2.7/site-packages/otopi/transaction.py", line 156, in __exit__
    self.commit()
  File "/usr/lib/python2.7/site-packages/otopi/transaction.py", line 148, in commit
    element.commit()
  File "/usr/share/ovirt-hosted-engine-setup/scripts/../plugins/gr-he-common/vm/boot_disk.py", line 219, in commit
    self._injectBackup()
  File "/usr/share/ovirt-hosted-engine-setup/scripts/../plugins/gr-he-common/vm/boot_disk.py", line 154, in _injectBackup
    g.add_drive_opts(filename=destination, format='raw', readonly=0)
  File "/usr/lib64/python2.7/site-packages/guestfs.py", line 559, in add_drive
    r = libguestfsmod.add_drive (self._o, filename, readonly, format, iface, name, label, protocol, server, username, secret, cachemode, discard, copyonread)
RuntimeError: /rhev/data-center/mnt/10.0.0.1:_data_nfs/c65acd3e-2ed8-46b6-8be9-a6d472c35441/images/1554afb0-1b74-497b-9d23-de7eed355595/c29d4ad0-ccf7-4863-a504-0bef62e6988c: Permission denied