e2etest: use navigator.webdriver flag to detect e2e context
e2etest: use navigator.webdriver flag to detect e2e context

Former-commit-id: 88d66f73462b6501a51438d5ae5119cb5938557f
alisman/cbioportal-frontend,cBioPortal/cbioportal-frontend,alisman/cbioportal-frontend,alisman/cbioportal-frontend,alisman/cbioportal-frontend,alisman/cbioportal-frontend,cBioPortal/cbioportal-frontend,cBioPortal/cbioportal-frontend,cBioPortal/cbioportal-frontend,cBioPortal/cbioportal-frontend,cBioPortal/cbioportal-frontend,alisman/cbioportal-frontend