ctld: Support anonymous LUN entries in UCL

[jhb]

Summary

If a target LUN entry doesn't have a name property, assume it is an
anonymous LUN and parse other properties from the entry to define the
LUN.

This removes the odd support for target LUNs only named by an integer.
My guess is this was meant to implement support for anonymous LUNs
based on how the syntax for this works in the non-UCL case, but the
prior implementation was useless (it just created unconfigured LUNs).