Fix a sphinx docs error

Comment out specs/juno/* until a spec merges so that the docs can
build without errors.

There is still one warning about man pages with this change in place,
but I believe it will require a change to pbr to suppress.

Change-Id: Id63da83ce6e60c444322072e68c17c97cf983846
Make sphinxbuild fail on formatting errors

This change will cause docs build to fail if rst is badly formatted.

Change-Id: I20e31fb25717388c22c54d5109afc4a56f9ab28d
Allow running 'tox' with no arguments

Change-Id: I3137ce5ae5631bf5bcf0455a17828369dea6b9fd