Test for multiple appliance update (rebased & updated apagac's PR)

Add multiple appliance update workflow

Update redhat_updates page

Add redhat_updates to cfme_data yaml

Add rhsm, sat5, sat6 and proxy to credentials yaml

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Currently supports only RHSM, Sat5 and Sat6 (tested only with RHSM atm)

TODO:
  - RH Mirror feature (content proxy)