Added step to make sure 'root_helper' key references 'neutron'

In the current Neutron Havana packages for RHEL-style distributions,
the default 'root_helper' key in neutron.conf references 'quantum'
instead of 'neutron'. This issue should get fixed upstream, but in
the meantime I added a step to make sure this key references
'neutron'.

Change-Id: I25f9faaba1067040829633aff990d238f5bf4ced
backport: havana
Closes-Bug: #1258309
Image Guide: Mention hw_video_model image property

This property is specific for the Libvirt driver.

Change-Id: I5dd74d859029dd74ce84cce48a8d3d70e2337e13
Closes-Bug: #1260093
Merge "Added step to make sure 'root_helper' key references 'neutron'"
Merge "Image Guide: Mention hw_video_model image property"