Make CI run PHPUnit tests

- Uses PHP 7.4 docker image and composer.

.gitlab-ci.yml

 stages:
-- marcus_test
+- test
+- deploy_to_test
+
+phpunit:
+  stage: "test"
+  image: "php:7.4"
+  before_script:
+  - apt-get update -yqq
+  - apt-get install -y git zip
+  - curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
+  - composer install
+  script:
+  - ./vendor/bin/phpunit
+  tags:
+  - spes
+  cache:
+    key: $CI_COMMIT_REF_SLUG
+    paths:
+    - "vendor/"
 
 marcus_test:
   variables:
     MARCUS_SERVER: $MARCUS_TEST_SERVER_IPV6
   image: oyvindlg/gitlab-ci-library:ansible-cgi
-  stage: "marcus_test"
+  stage: "deploy_to_test"
   before_script:
   - eval $(ssh-agent -s)
   - echo $MARCUS_TEST_KEY | base64 --decode | ssh-add -
 
   script:
   - echo "debug"
-  - ssh -6 -o "StrictHostKeyChecking=no" $MARCUS_USER@$MARCUS_SERVER "cd $MARCUS_HOME && git fetch && git checkout $CI_COMMIT_SHA && composer install --no-dev" 
+  - ssh -6 -o "StrictHostKeyChecking=no" $MARCUS_USER@$MARCUS_SERVER "cd $MARCUS_HOME && git fetch && git checkout $CI_COMMIT_SHA && composer install --no-dev"
   - ssh -6 -o "StrictHostKeyChecking=no" $MARCUS_USER@$MARCUS_SERVER "cd $ADMIN_HOME && git fetch && git checkout $CI_COMMIT_SHA && composer install --no-dev"
-
   tags:
   - spes
-