Check for backing lun on iscsi target create

Check to verify the backing lun was actually created and not just
the controller lun.  If it was NOT created, attempt to issue
tgtadm --op new to see if we can recover.

If this fails, then we want to actually fail in Cinder rather than
pretending that everything went well, so we'll log the error and raise.

Change-Id: I3cabab0d214c051267638a627664df2b673236e3
Closes-Bug: #1226337
Merge "Check for backing lun on iscsi target create"