RFR: bot: add work item name to counters

[Erik Helin]

Hi all,

please review this patch that adds a new label to the counters in `BotRunner` - `work-item`. The `work-item` label shows the name of the work item (in addition to the bot name which is already present in the `bot` label). This is useful for metrics from larger bots that consists of multiple work items.

Thanks,
Erik

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Depends on: https://git.openjdk.java.net/skara/pull/1168

Commit messages:
 - bot: add work item name to counters

Changes: https://git.openjdk.java.net/skara/pull/1169/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=1169&range=00
  Stats: 9 lines in 1 file changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/skara/pull/1169.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1169/head:pull/1169

PR: https://git.openjdk.java.net/skara/pull/1169