Fix random failures on preview Web UI ftests

23:44:42 [INFO]      [exec] 1 failing
23:44:42 [INFO]      [exec] 1) Previewer for File document with different types of blobs as content37 I login as "John":
23:44:42 [INFO]      [exec] unknown error: session deleted because of page crash
23:44:42 [INFO]      [exec] from unknown error: cannot determine loading status
23:44:42 [INFO]      [exec] from tab crashed
23:44:42 [INFO]      [exec] running chrome
23:44:42 [INFO]      [exec] Error: An unknown server-side error occurred while processing the command.
23:44:42 [INFO]      [exec]     at Login.set (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/pages/login.js:6:12)
23:44:42 [INFO]      [exec]     at World.<anonymous> (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/features/step_definitions/login.js:30:5)
23:44:42 [INFO]      [exec]     at new Promise (node_modules/core-js/library/modules/es6.promise.js:177:7)
23:44:42 [INFO]      [exec]     at element("* >>> #username") - at Object.el.element (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/features/step_definitions/support/shadowdom.js:60:52)

10:30:15 [INFO]      [exec] 1) Previewer for File document with different types of blobs as content37 I login as "John":
10:30:15 [INFO]      [exec] chrome not reachable
10:30:15 [INFO]      [exec] running chrome
10:30:15 [INFO]      [exec] Error: Request timed out after the element was still found on the page.
10:30:15 [INFO]      [exec]     at World.<anonymous> (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/features/step_definitions/login.js:34:18)
10:30:15 [INFO]      [exec]     at new Promise (node_modules/core-js/library/modules/es6.promise.js:177:7)
10:30:15 [INFO]      [exec]     at url("ui") - at Function.get (node_modules/@nuxeo/nuxeo-web-ui-ftest/test/pages/ui.js:86:12)