L2SS-259: Use alpine Linux docker image for building

.gitlab-ci.yml

@@ -13,7 +13,9 @@ stages:
   - unit-tests
 building:
   stage: building
-  image: ubuntu:20.04
+  image: docker
+  services:
+    - docker:dind
   variables:
     CHECKOUT_DIR: "$CI_PROJECT_DIR/../"
     TANGO_SKA_LOCAL_DIR: "${CHECKOUT_DIR}"
@@ -25,8 +27,7 @@ building:
     TANGO_CONTAINER_ENV: "-e TANGO_SKA_CONTAINER_DIR=${TANGO_SKA_CONTAINER_DIR} -e TANGO_LOFAR_CONTAINER_DIR=${TANGO_LOFAR_CONTAINER_DIR}"
     NETWORK_MODE: "lofar"
   before_script:
-    - sudo apt-get update
-    - sudo apt-get install -y git make docker-compose
+    - apk add --no-cache docker-compose make
     - touch ~/.Xauthority
   script:
     - cd docker-compose