POST /user sample response
Replace all path variables
Carry sample response definition :id to response

The id is used to inject one sample response into another one. This
cannot happen until the actual response is loaded. For this reason, the
loaded response needs to have the id so we are able to perform the
mapping later
Don't return anything from the defsample macro

Functions with side-effects should not return anything. In this
particular case, there were problems because returning the data built by
the macro caused the sexps to be prematurely evaluated, defeating the
whole purpose of the late bindings of sample responses.

This one hurt.
Add :id to user post sample response