Adds step-12 about roles

Adds symlinks to last chapter and doc
Added doc about linking the last "real" chapter to the final chapter.
Improves suite test script
Added parameter support to test a single step
Added multiline summary support (roles)
Added role chapter
Added expectations for testing

Adds chapters 12 and 99

Adding a chapter just requires adding symlinks to hosts and site.yml to
the last chapter :
    cd step-99 && ln -sf
    ../step-<last>/{hosts,roles,site.yml,group_vars,host_vars} .
where last is the last chapter except final 99 (fixes #12).
Added step-12 about roles and a site.yml (fixes #21)

Adds more explanations on step-99