agl-compositor: Extend test case to include SDK images

Since agl-compositor can be run in SDK images to facilitate development,
update the test case accordingly.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

test-cases/agl-compositor.yaml

@@ -3,6 +3,7 @@ metadata:
   format: "Apertis Test Definition 1.0"
   image-types:
     target:  [ armhf, amd64 ]
+    sdk:  [ amd64 ]
   image-deployment:
     - APT
   type: functional
@@ -27,6 +28,9 @@ metadata:
     - "@agl-compositor-pavucontrol-screenshot.png"
 run:
   steps:
+    - "Only in case of an SDK image, switch to a new terminal and launch agl-compositor"
+    - "In case of target images this step is not required since agl-compositor starts at boot"
+    - $ agl-compositor
     - "Verify that a desktop shows in screen"
     - "Click the indicator for clock and volume in the bottom left to display a popup with additional information"
     - "Click the launcher button in the top left to display the available apps"