Can't help but notice DefaultNodeVersion and DefaultNpmVersion are hardcoded in the constant in this file.    For DefaultNodeVersion, we should have a tracking bug to adjust it in Public Kudu once we ship S25QFE.   However, Private Kudu should already use the latest one (0.10.21).

For DefaultNpmVersion, we have two choices.  1. hardcode it as well but with a comment to adjust together with DefaultNodeVersion.  2. look at npm text of corresponding default Node.   1 is more optimized but room for human error.  thought?