Destroy Datera export target after detach

Since there is only one lun associated with each target export object in
the Datera backend, we will destroy the target export object after
detaching the volume so they don't build up. This patch also fixes some
missing values for formatted strings.

Closes-Bug: #1368381
Change-Id: Id44ac4bb385ab39af50865a295938861ca977fa3
Merge "Destroy Datera export target after detach"