Support nested TOSCA functions in get_input

[loicalbertin]

As: TOSCA Component dev
I want to: use the get_input TOSCA function with nested TOSCA functions
So that: I can build complex stuff like { get_input: [ concat: [get_property: [SELF, input_base_name], "_v1"]]}

AC1: Similarly to #777, a limitation in Alien4Cloud prevent to use something else than a scalar as parameter of the get_input function. Apart from that this feature is already functional in Yorc. So we propose to introduce an alias to the get_input function called get_input_nf (nf for nested functions) that will not be handled and rejected by Alien.