Collected comments on metadata

[mattmathis]

Some of these should be pulled out into separate bugs, but most can be killed in one blow.

Metadata record has Starttime but Timestamp is zero time (could be StartTime or null) Metadata record does not indicate server name (nor does the RawIDM record)

Although I understand why redundant normative metadata might be a bug (server name does appear in the enclosing filename), there is a level of debugging/auditing that can't be supported without it.

The per .zst file metadata is also the right place to collect platform hardware and software UUIDs.