CVE-2022-1615 util/genrand: don't ignore errors in random number generation

Since we began using GnuTLS in genrand.c, we have ignored return values.

A failure of randomness is a very bad thing, and we have no option but to abort.

In https://bugzilla.samba.org/show_bug.cgi?id=15103 we considered whether this is a security issue, but ultimately decided the cases where this fails belong in the "already completely screwed" basket.

There's also a piggybacking patch for better reporting of uptodateness errors in samba-tool.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• (optional, if backport required) Bugzilla bug filed and BUG: tag added
• CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code