title: Multiple onPrepare or dynamic login params when using multiCapabilites
body: <p>basically the same as this: <a href="https://stackoverflow.com/questions/25163674/can-you-do-multiple-onprepares-per-browser-instance">https://stackoverflow.com/questions/25163674/can-you-do-multiple-onprepares-per-browser-instance</a> but since there were no answers or comments I'll post again.</p>
  
  <p>I want to login with two user profiles on two separate browsers. </p>
  
  <p>I'd be using something like this in my config file:</p>
  
  <pre><code>multiCapabilities: [{
      browserName: 'chrome',
      specs: ['profile_1.spec.js'],
      login: {email: 'profile_1',
      password: 'pw1'}
  }, {
      browserName: 'chrome',
      specs: ['profile_2.spec.js'],
      login: { email: 'profile_2',
      password: 'pw2'}
  }]
  </code></pre>
  
  <p>Since my login page isn't angular I need to use onPrepare and I can only set login params once.</p>
  
  <p>Is there a way pass the login params from the multiCapabilities array to the onPrepare function or to have specific onPrepares inside the multiCapabilities objects?</p>