Allow including qtbase instruction yaml files in qt5 product

I'm trying to implement calling the CMake configure step for qt5.git, without building, similar how it's done with qmake for qt5.git.

To do that, I need to include instruction .yaml files from qtbase.

version: 2
accept_configuration:
  condition: property
  property: host.os
  equals_property: target.os

instructions:
  Build:
    - !include "{{qt/qtbase}}/prepare_building_env.yaml"
    - ....

Currently that does not work because qtbase is not a dependency of qt5.

Two approaches were proposed:
1) Make qt5 depend on all its submodules. Consequence that qt5 can't be built before all the other dependencies.

2) Allow inclusion of instruction files by relative path.

 - !include ""../../qtbase/coin/instructions/my.yaml"

This is needed to avoid even more copy-pasting of instructions between repos.