Fix cloud migration status auth filtering (#1273)
Fix cloud migration status auth filtering (#1273)

driver.Enumerate, when given a list of volume Ids, will return
NotFound and an empty list if any volumes do not exist. Now,
we enumerate each volume one by one to avoid this when filtering
for cloud migrate status permissions.

Signed-off-by: Grant Griffiths <7561d7b6fa252e14d948ef730f22c68c9d861f6b@portworx.com>
libopenstorage/openstorage,libopenstorage/openstorage,libopenstorage/openstorage