SOLR-14443: Make SolrLogPostTool resilient to odd requests

[gerlowskija]

Description

SolrLogPostTool is relatively brittle in how it indexes log records to Solr. A single error from Solr causes the tool to crash. Further, when user requests have duplicate or unnecessary parameters, the tool attempts to record all of these (even when the field used is singlevalued).

As a result, a single "oddball" request crashes the whole ingestion run.

Solution

This PR makes two related changes. First, it changes SolrLogPostTool's batching code to log (but ultimately ignore) errors. This allows an indexing run to survive malformed records or other indexing blips. Second, it changes the record-parsing code to only record single values for single-valued log record fields. This prevents a common cause of malformed records.

Tests

Manual testing, in addition to a test case added to SolrLogPostToolTest

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the master branch.
• I have run ant precommit and the appropriate test suite.
• I have added tests for my changes.
• I have added documentation for the Ref Guide (for Solr changes only).