Build: Change submodule CI updating

The clone operation on Travis will already update the submodules. The
checkout is all that is required to reset the headless repo in the
folder to the latest commit.
Merge pull request #2511 from nschonni/fix-submodule-updates

Build: Change submodule CI updating
Build: Init submodule for Travis demo building

Use the already cloned wet-boew-dist to save the extra full clone. There
are notes on using the --reference command on
https://www.kernel.org/pub/software/scm/git/docs/git-clone.html, but
those shouldn't be affected by this usage.
Merge pull request #2540 from nschonni/init-submodules-for-demo-updates

Build: Init submodule for Travis demo building
Merge branch 'v3.0'