RFR: 1603: Make labels handling consistent in all Issue implementations [v2]

[Zhao Song]

> Make TestIssue and JiraIssue update the cache when updating labels.

Zhao Song has updated the pull request incrementally with one additional commit since the last revision:

  Adjusted format and updated setLabels in JiraIssue and TestIssue

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Changes:
  - all: https://git.openjdk.org/skara/pull/1387/files
  - new: https://git.openjdk.org/skara/pull/1387/files/05319b17..b26f73b8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1387&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1387&range=00-01

  Stats: 9 lines in 2 files changed: 2 ins; 3 del; 4 mod
  Patch: https://git.openjdk.org/skara/pull/1387.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1387/head:pull/1387

PR: https://git.openjdk.org/skara/pull/1387