Merge branch 'ci/improve-ci-steps' into '2.x'

Use docker executor to run health check and sonar

Fix the `.gitlab-ci.yml` to properly run a simple health check, and a [SonarQube](http://sonarqube.org/) static analysis.


The SonarQube instance runs at https://sonarqube.savoirfairelinux.net/. Credentials to login are available in SFLvault (m#2222)

See merge request !18

.gitlab-ci.yml

+stages:
+  - test
+  - quality
 health-check:
+  image: python:2.7
+  stage: test
   script:
+    - pip install fabric
     - fab --version
     - fab -f . --list-format=nested --list
-sonar:
+  tags:
+    - docker-images
+sonarqube:
+  image: ntdt/sonar-scanner:2.7
+  stage: quality
   script:
-    - /opt/sonar-scanner/bin/sonar-scanner -Dsonar.host.url='https://sonarqube.savoirfairelinux.net' -Dsonar.login='8317c73bde6903c2cca1fbcc2148a937602fbc97' -Dsonar.analysis.mode=preview -Dsonar.issuesReport.console.enable=true     -Dsonar.gitlab.commit_sha=$CI_BUILD_REF -Dsonar.gitlab.ref=$CI_BUILD_REF_NAME
-
-
+    - cd $CI_PROJECT_DIR && /opt/sonar-scanner/bin/sonar-scanner -Dsonar.host.url=$SONAR_HOST -Dsonar.login=$SONAR_TOKEN
+  tags:
+    - docker-images