docs: Rewrite a few awkward sections

docs: Rewrite a few awkward sections

Address several oddities, and bring them in line with the style
used for the vast majority of our documentation. In a couple of
cases, some of the possible values for an attribute were listed
with :since: information matching that off the attribute itself,
making it redundant.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>