Don't use oslo's _sanitize_default

This method disappeared from oslo, so provide our own sanitizer. This is
needed for now but can be removed as soon as projects provide
Opts.sample_default values.

Change-Id: I13e76c75a74667fa9bd3c779a6cf45d0281ed680
Closes-Bug: #1341250
Merge "Don't use oslo's _sanitize_default"