model.adoc issues

[sandrobonazzola]

While serving model.adoc on oVirt webstie, jackyll reports:

asciidoctor: WARNING: model.adoc: line 57033: id assigned to section already in use: use-elements-instead-of-attributes-in-vcpu-pin
asciidoctor: ERROR: model.adoc: line 86: level 0 sections can only be used when doctype is book
asciidoctor: ERROR: model.adoc: line 471: level 0 sections can only be used when doctype is book
asciidoctor: ERROR: model.adoc: line 1192: level 0 sections can only be used when doctype is book
asciidoctor: ERROR: model.adoc: line 56457: level 0 sections can only be used when doctype is book
asciidoctor: ERROR: model.adoc: line 56606: level 0 sections can only be used when doctype is book
asciidoctor: WARNING: model.adoc: line 57033: id assigned to section already in use: use-elements-instead-of-attributes-in-vcpu-pin