Fix add_mapped_luns functionality in LUN ui_command_create
Fix add_mapped_luns functionality in LUN ui_command_create

Rewrote all the code. Tries to use TPG LUN number for mapped LUN number
unless it's already used, in which case it looks for an unused mlun #.

Improve info text a little to give LUN and MLUN values.

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

cvubrugier/targetcli-fb,cloud4life/targetcli-fb,agrover/targetcli-fb