An empty distro value leads to OVERRIDES and FILESOVERRIDES containing
"::" entries which causes odd issues such as files being included when
they shouldn't be. We could put in anonymous python to guard against
empty entries but its messy and setting a default value for DISTRO to
something harmless is much easier.
This patch adds a weak default and ensures the sanity test doesn't
complain about it.
DISTRO_VERSION and SDK_VERSION are also updated to match.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
