CI: stability / cosmetics improvements

-- Stability issues when installing packages for USRP variants on new VM
     It sometimes timed-out
     Added loop up to 5 tries to add apt-repository
  -- Temporary merge during MergeRequest processing now returns an
     error when there are any conflicts
     Will stop the whole build
  -- Physical simulator now has a XLST for the XML result

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

ci-scripts/Jenkinsfile-gitlab

@@ -45,6 +45,12 @@ pipeline {
                     }
                 }
             }
+            post {
+                failure {
+                    def message = "OAI " + JOB_NAME + " build (" + BUILD_ID + "): Merge Conflicts -- Cannot perform CI"
+                    addGitLabMRComment comment: message
+                }
+            }
         }
 
         stage ("Start VM -- cppcheck") {
@@ -176,6 +182,7 @@ pipeline {
                         if(fileExists('archives/vm_tests_logs.zip')) {
                             archiveArtifacts artifacts: 'archives/vm_tests_logs.zip'
                             archiveArtifacts artifacts: 'archives/*/test/results_autotests*.xml'
+                            archiveArtifacts artifacts: 'archives/*/test/*.xsl'
                         }
                     }
                 }