add belongs_provide_ret attribute to Variable
In smart, we don't validate variables belonging to provide_ret. We then
consider they will be filled correctly at deployment time. The
agent will still validate these variables before using them.
Don't return variables that will be filled by smart but create a xpath that designates the value that smart will have to use.
Merge branch 'provide_ret'.

Conflicts:
	armonic/client/smart.py