engine service add stack_user_project_id to create_stack interface

Adds the option to pass stack_user_project_id to align with the recent
change which makes nested stacks inherit the stack user project from
their parent ref bug #1343163.  This will enable the same behavior to
be maintained when creating stacks via RPC calls instead of directly.

Change-Id: I2a102722d3e5228ccbb71ca13f4246725626f5a9
blueprint: decouple-nested
Add stack_user_project_id to _create_stack RPC interface

Adds the ability to pass the parent stack_user_project_id into nested stacks
when creating them via RPC, so we can maintain the recently introduced
behavior where the parent stack user project is inherited by nested
stacks.

Change-Id: I425e80cfc8f9c646ade7d47f202744103142ab55
blueprint: decouple-nested
Merge "engine service add stack_user_project_id to create_stack interface"
Merge "Add stack_user_project_id to _create_stack RPC interface"