Fix LHN driver to allow backend name configuration

The LHN driver wasn't allowing custom volume_backend_name to be set
via multi-backend configuration input.  In addition there were some
issues with the updating that are also addressed in this patch.

There are other drivers that are going to need updated/fixed for
this same problem, but those will be addressed in a separate patch/bug.

Fixes bug: 1173037

Change-Id: Iae247a500739d02e145511ebe96dddaff8966419
Remove old_name from kwargs when using IET helper.

The IET driver passes the input kwargs from export
directly to the IET driver, but one of the keys here
is specifically for migration and a bug associated with
going from nova-vol to cinder-uuid's.

This patch just checks in the IET code if we have the key set
and if so pops it out before passing through to iet.

Fixes bug: 1175207

Change-Id: I965bdfbe078d61b906aebc48961c1806a9fb0c59
Merge "Remove old_name from kwargs when using IET helper."
Merge "Fix LHN driver to allow backend name configuration"