Install Scripts - Doc: Add prerequisites and clarify configuration step

Add 2 missing prerequisites for installing the plugin and importing the
base box (for both AWS/EC2 and Rackspace)

Break configuration out to automated and manual and make the reference
to the setup*.sh script more explicit.

Change-Id: Ieb7be311ebfef6a0e5f29ed55edb123ac3598a18
Merge "Install Scripts - Doc: Add prerequisites and clarify configuration step"