Fix bind mount of glance images
Fix bind mount of glance images

Bind mount should be created when glance_nfs_client is
either undefined OR empty

Change-Id: I59b183dc376fd64300d088c9831fe5ea2e7412f0
Closes-Bug: #1638907
(cherry picked from commit 677ceb20a589b4262394ca9765ec23394082c8d1)

yanyao/newton,yanyao/newton