RFR: 2451: Skara bot fails to transition bug to Resolved due to empty response from api

[Zhao Song]

A user reported that one backport issue was not automatically resolved by the Skara bot. From the logs, Erik found that the bot didn't actually send the request to transition the bug to resolved and he noticed that around that time, the bot was renewing the access token for jbs.

When updating the state of an issue, the Skara bot first attempts to fetch the available transitions for that issue by calling this API:
https://bugs.openjdk.org/rest/api/2/issue/issue_id/transitions.

I called the API without authentication, I was expecting a 401 Unauthorized response. However, I received an empty response:
`{"expand":"transitions","transitions":[]}.`

Due to this empty response, the Skara bot did not attempt to transition the bug to any state.

In my opinion, availableTransitions would be empty only when requesting the API without authentication,  so skara bot would throw an exception in this case.

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Commit messages:
 - SKARA-2451

Changes: https://git.openjdk.org/skara/pull/1706/files
  Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1706&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2451
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/skara/pull/1706.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1706/head:pull/1706

PR: https://git.openjdk.org/skara/pull/1706