Sphinx 1.6.x gained a cross-reference check warning that caused
the build to fail in "tox -e docs" environment. Removing underscores
from the citation reference identifier ensures that the cross references
are properly detected. Similarly missing references to footnotes are
now a warning (which is upgraded to an error in the docs tox
environment) so adjust references where it makes sense and is needed.
Closes-Bug: #1695127
Change-Id: I7e55dcf910e0ba6dd85b565db8cb1ecbdd39634a
77b2ae9c5f