Update _resize_volume_file() to support appropriate permissions

ibmnas driver inherits _set_rw_permissions_for_all() from nfs.py
which sets 666 to the volumes. Changes are expected to be made in
nfs.py such that it sets 600 or 660 permissions, by doing so
ibmnas driver fails performing the operation _resize_volume_file()

Adding run_as_root in resize_volume operation.

Change-Id: Iecaf111f96f93b4e24bd81edd6aa82829113b4bb
Closes-Bug: #1333252
Merge "Update _resize_volume_file() to support appropriate permissions"