Fix configurations such as 'dist' and tar building

For config targets such as 'dist', which doesn't have a BASE template,
we still need to have a default build scheme.

Additionally, the unified Makefile template's target 'tar' wasn't
quite as flexible as the unixmake one.

Finally, .travis-create-release.sh can be somewhat simplified now that
it builds with the unified build scheme.

Reviewed-by: Matt Caswell <matt@openssl.org>