introduce variable

roles/matrix-base/defaults/main.yml

@@ -66,3 +66,7 @@ run_setup: true
 run_self_check: true
 run_start: true
 run_stop: true
+
+# Building every docker image from source on the target host
+# Controlling docker image build is possible on a per unit base
+matrix_container_images_self_build: false