Fix 9.10 Web UI functional tests

https://qa2.nuxeo.org/jenkins/job/9.10/job/plugins_nuxeo-web-ui-2.2_9.10/ is failing since October 19th 2019.

Different failures visible:

• Content Preview

  Error: element ("nuxeo-home") still not existing after 10000ms
      at Home.get (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/pages/base.js:10:12)
      at Home.waitForVisible (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/pages/base.js:19:12)
      at World.<anonymous> (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/features/step_definitions/login.js:35:18)
      at new Promise (node_modules/core-js/library/modules/es6.promise.js:177:7)
      at execute(<Function>, "nuxeo-home", true, , ) - wdio-shadow-plugin.js:174:10
  

  Screenshot is showing a blank screen.

• Search

  Error: element ("nuxeo-menu-icon[name='defaultSearch']") still not visible after 10000ms
      at Drawer.open (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/pages/ui/drawer.js:66:15)
      at World.<anonymous> (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/features/step_definitions/ui.js:4:72)
      at new Promise (node_modules/core-js/library/modules/es6.promise.js:177:7)
      at execute(<Function>, "nuxeo-menu-icon[name='defaultSearch']", true, [object Object], ) - wdio-shadow-plugin.js:174:10
  

  Screenshot shows home page with degraded theme...

• Task

  AssertionError: expected false to be true
      at World.<anonymous> (/opt/jenkins/workspace/9.10/plugins_nuxeo-web-ui-2.2_9.10/ftest/web-ui/webdriver/node_modules/@nuxeo/nuxeo-web-ui-ftest/test/features/step_definitions/tasks.js:50:5)
      at new Promise (/opt/jenkins/workspace/9.10/plugins_nuxeo-web-ui-2.2_9.10/ftest/web-ui/webdriver/node_modules/core-js/library/modules/es6.promise.js:177:7)