title: login failed with behat even the field names are correct
body: <p>I tried to login <a href="https://testinternal.com/login" rel="nofollow noreferrer">https://testinternal.com/login</a> (internal website) with behat but I got the following error. I used Firefox developer to check the text field names, the field names are correct with username and password fields. Any ideas why it failed?</p>
  
  <blockquote>
    <p>13:40:34.128 INFO - Executing: [get: <a href="https://testinternal.com]" rel="nofollow noreferrer">https://testinternal.com]</a>)
    13:40:34.249 INFO - Done: [get: <a href="https://testinternal.com/logon]" rel="nofollow noreferrer">https://testinternal.com/logon]</a>
    13:40:34.251 INFO - Executing: [find elements: By.xpath:
    //html/.//<em>[self::input | self::textarea | self::select][not(./@type =
    'submit' or ./@type = 'image' or ./@type = 'hidden')][(((./@id =
    'username' or ./@name = 'username') or ./@id =
    //label[contains(normalize-space(string(.)), 'username')]/@for) or
    ./@placeholder = 'username')] |
    .//label[contains(normalize-space(string(.)),
    'username')]//.//</em>[self::input | self::textarea |
    self::select][not(./@type = 'submit' or ./@type = 'image' or ./@type =
    'hidden')]]) 13:40:34.270 INFO - Done: [find elements: By.xpath:
    //html/.//<em>[self::input | self::textarea | self::select][not(./@type =
    'submit' or ./@type = 'image' or ./@type = 'hidden')][(((./@id =
    'username' or ./@name = 'username') or ./@id =
    //label[contains(normalize-space(string(.)), 'username')]/@for) or
    ./@placeholder = 'username')] |
    .//label[contains(normalize-space(string(.)),
    'username')]//.//</em>[self::input | self::textarea |
    self::select][not(./@type = 'submit' or ./@type = 'image' or ./@type =
    'hidden')]]</p>
  </blockquote>
  
  <pre><code>    Feature: Sign in to the website
      In order to access the administrative interface
          As a visitor
          I need to be able to log in to the website
  
       @javascript
        Scenario: Log in with username and password                     # features/signin.feature:7
          Given I am on "/logon"                                        # Behat\MinkExtension\Context\MinkContext::visit()
          When I fill in the following:                                 # Behat\MinkExtension\Context\MinkContext::fillFields()
            | username | testuser |
            | password | testpwd  |
            Form field with id|name|label|value "username" not found.
          And I press "Sign in"                                         # Behat\MinkExtension\Context\MinkContext::pressButton()
          Then I should be on "http://testinternal.com"                 # Behat\MinkExtension\Context\MinkContext::assertPageAddress()
          And I should see "My Flows"                                   # Behat\MinkExtension\Context\MinkContext::assertPageContainsText()
  
      2 scenarios (2 failed)
      10 steps (2 passed, 6 skipped, 2 failed)
  </code></pre>