Added ndmp fixes for getting info from Veritas Backup Exec Agent 15 and 16.

[xorrbit]

When scanning Veritas Backup Exec Agent 15 or 16 port 10000 (ndmp), both ndmp-version.nse and ndmp-fs-info.nse throw errors.

Veritas returns a NOT_AUTHORIZED_ERROR response on both these versions when doing either a get hostinfo request (which is done in ndmp-version.nse), or a get fsinfo request (done in ndmp-fs-info.nse).

This commit adds some checking for that error code in the header and some simple handling in that case. Curiously enough, it replies properly to a get serverinfo request without any authentication, so ndmp-version.nse is still useful in this case.

Here's a gist with a sanitized debug scan before the changes, which shows the errors, and after, which shows how it is now handled: https://gist.github.com/xorrbit/9b149f6074a8339fd5bcf6a467a4f557