Asciidoctor.include.for.dry.doc

As discussed in mailing list:
http://aerogear-dev.1069024.n5.nabble.com/aerogear-dev-ag-org-Make-our-doc-even-dryer-td6261.html
and
http://aerogear-dev.1069024.n5.nabble.com/aerogear-dev-Asciidoc-snippet-Git-hook-td6395.html#a6519

With this PR I remove duplicate documentation bits. 
Also this PR will be useful to include cookbook source code in aerogear revamp (sass branch could be rebased after this PR get merged)