Run nightwatch e2e tests on gitlab CI

CI script:

package.json :

test:e2e:headless : "vue-cli-service test:e2e --config ./tests/e2e/main-test/nightwatch.conf.js --env chromeHeadless "

“dependencies”: {
“chromedriver”: “2.46.0”,
“selenium-server”: “3.9.0”
}

nightwatch config :

  selenium: {                                                                                      
     start_process: true,                                                                           
     server_path: require('selenium-server').path,                                                  
     port: 4449,                                                                                    
     cli_args: {                                                                                    
       'webdriver.chrome.driver': require('chromedriver').path                                      
     }                                                                                              
   },                                                                                               
                                                                                                    
   test_settings: {                                                                                 
     default: {                                                                                     
       selenium_port: 4449,                                                                         
       selenium_host: 'localhost',                                                                  
       silent: true,                                                                                
       globals: {                                                                                   
         devServerURL: 'http://localhost:' + config.devServer.port                                  
       }                                                                                            
     },                                                                                             
     chromeHeadless: {                                                                              
       desiredCapabilities: {                                                                       
         browserName: 'chromeHeadless',                                                             
         javascriptEnabled: true,                                                                   
         acceptSslCerts: true,                                                                      
         chromeOptions: {                                                                           
           args: [                                                                                  
             'headless',                                                                            
             'disable-gpu',                                                                         
             'no-sandbox'                                                                           
                                                                                                    
           ]                                                                                        
        }                                                                                          
       }                                                                                            
      }