(MCO-445) Remove saucy from build defaults

This commit removes saucy from build_defaults. It went EOL July 17,
2014.
(maint) Update build defaults

This removes sid and unstable from build_defaults because we no longer
support it.
Merge pull request #233 from clantant/MCO-445/stable/saucy

(MCO-445 & maint) update build defaults