[NaCl SDK] Don't create SDK tarball by default.

This will make the build-only trybots faster and also
local developer builds faster (in most cases the tarball
creation is not needed on a developers desktop).

R=binji@chromium.org

Review URL: https://codereview.chromium.org/31103002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229814 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229814