Feature Request: Improve VStream Error Messages

[twthorn]

Feature Description

VStream errors often are not clear what occurred and which components of the system were involved (eg which vtgate, vttablet). Some examples of these errors are:

Exception status: Status{code=UNKNOWN, description=target: <keyspace>.c0-.replica: vttablet: rpc error: code = Unknown desc = EOF, cause=null}
unexpected server eof

Here are a possibilities to improve the information sent in VStream errors:

1. Include the tablet hostname (many times the issue is with the specific mysql/host so this is the first step of debugging)
2. Return the original mysql error (often checking mysql error.log returns the actual root cause). There may be cases we obfuscate these errors

Use Case(s)

Helps operators of VStream clients to debug/fix things