CI: pipeline yocto: Change scope of CI_PARAM_IMAGE, ... to fix fngsystem build

The variables CI_PARAM_IMAGE, CI_PARAM_DISTRO, CI_MACHINE have been
defined outside the job in the '.gitlab-ci.yml' file. This has a lower
precedence then variables defined inside the job, but it seems that
these variables are used in the scope of 'Trigger variables' when
available in the trigger job. These override the value set in the
template. As main results this made FNGSystem jobs build the normal
yocto.

docs/manifest-pipeline.md

@@ -45,7 +45,9 @@ dynamic-child-pipeline feature. [See gitlab docs.][1]
 
 There is a *'generate-build-jobs'* job, that creates a yaml file containing the
 pipeline with all needed jobs.
-There are the following CI variables controlling the content:
+There are the following CI variables in the 'generate-build-jobs' job controlling
+the content (make sure these are not set in a more global scope, as this 
+would overwrite the settings in the generated yml):
 
 * `CI_PARAM_MACHINES`: Space separated list of machines to build for, like "santaro santoka" 
 * `CI_PARAM_IMAGE`: The name of the image to build. If set to an empty string, 

manifest-pipeline-yocto.yml

@@ -18,16 +18,18 @@ variables:
   # This is the jinja2 template file used to generate the build jobs
   BUILD_JOBS_TEMPLATE: build-jobs-yocto.jinja2
 
-  # Default image and distro
-  CI_PARAM_IMAGE: guf-image
-  CI_PARAM_DISTRO: guf-wayland
+generate-build-jobs:
+  variables:
+    # Default image and distro
+    CI_PARAM_IMAGE: guf-image
+    CI_PARAM_DISTRO: guf-wayland
 
-  # Flash-N-Go image and distro
-  # In the past, the buildfng job overwrote the image and distro itself. Due to the
-  # transition to the new seconorth names, image and distro for the buildfng must be
-  # settable from outside of the job.
-  CI_PARAM_IMAGE_FNG: fngsystem-image
-  CI_PARAM_DISTRO_FNG: guf-fngsystem
+    # Flash-N-Go image and distro
+    # In the past, the buildfng job overwrote the image and distro itself. Due to the
+    # transition to the new seconorth names, image and distro for the buildfng must be
+    # settable from outside of the job.
+    CI_PARAM_IMAGE_FNG: fngsystem-image
+    CI_PARAM_DISTRO_FNG: guf-fngsystem
 
-  # List of machines to build images for
-  CI_PARAM_MACHINES: imx6guf imx6ullguf imx8mguf imx8mpguf
+    # List of machines to build images for
+    CI_PARAM_MACHINES: imx6guf imx6ullguf imx8mguf imx8mpguf