Removed virtualbox guide from index_contents.rst
Removed virtualbox guide from index_contents.rst

Removed the Running Mirantis OpenStack on VirtualBox document as duplicate

Change-Id: Iedbde647fff0a1a6a80f7f2c3fc8af1b310c61a2
Closes-Bug: #1498123

stackforge/fuel-docs,stackforge/fuel-docs