Cleanup

This (opinionated) pull request allows a user to run the samples exactly as outlined on http://zerovm.org/download.htm.

To do this, I've allowed defaults to be set on `$ZEROVM_ROOT` and `$ZVM_PREFIX`.

This also adds git ignores for files generated during a build/test.

This suite of samples could probably use some more love, let me know if you'd like me to have at it!