Add use_multipath_for_image_xfer with E-Series

This change implements the documented best practice to use multipath
with a Cinder deployment leveraging the NetApp E-Series driver by
setting a Cinder configuration setting to ensure that multipath is
appropriately used by the driver.

Change-Id: I4d279ebefc5a1ed935680775c6ea95fa38c1b9ef
Merge "Add use_multipath_for_image_xfer with E-Series"