CI: improve stability

-- Added apt-get update before any apt-get command in shell script on VM
     Necessary if the cloud image is a bit out of sync
  -- Added VM memory parameter when creating VM
     Necessary for cppcheck build
  -- Aligned some scripts with develop branch

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

ci-scripts/Jenkinsfile-gitlab

@@ -45,6 +45,14 @@ pipeline {
                     }
                 }
             }
+            post {
+                failure {
+                    script {
+                        def message = "OAI " + JOB_NAME + " build (" + BUILD_ID + "): Merge Conflicts -- Cannot perform CI"
+                        addGitLabMRComment comment: message
+                    }
+                }
+            }
         }
 
         stage ("Start VM -- cppcheck") {