Improve definitions of key terms in the Aquilon book
Improve definitions of key terms in the Aquilon book

The quattor.org website had some better definitions of the terminology
used in Aquilon so copy those definitions into the official book.

Change-Id: I574b7e2f53b794aa9980b179f35fc1a001cc2d34
Reviewed-by: Dave Reeve <6a84ee3ae0690d4584b99406fb3076392171f50e@morganstanley.com>

guillaume-philippon/aquilon,quattor/aquilon,quattor/aquilon,quattor/aquilon,guillaume-philippon/aquilon,guillaume-philippon/aquilon