Most of our projects using Sphinx are not Python projects so
building sdist does not make sense for them. Default docs to
skip it since folks working on Python projects are more likely
to know what this parameter means.
Change-Id: Ib38395954c2fba988480cd5774b0e7ac46499b91 Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>