Try to protect from StaleElementReferenceException in is_displayed

I noticed that this happened in last Jenkins build in `test_ldap_auth_and_roles.py`.

If the passed locator is retrievable multiple times (string, ...), it is tried multiple times. Ignored with WebElement, as it is already broken if it raises StaleElementException.
basically - "If we can look it up again, try doing it"

If it is a webelement, that is lost case already so no repeating happens.