RFR: 8350964: Add an ArtifactResolver.fetch(clazz) method [v2]

[Matthew Donovan]

> In this PR, I created a new method, `ArtifactResolver.fetchOne()`, to consolidate duplicate code across tests.

Matthew Donovan has updated the pull request incrementally with one additional commit since the last revision:

  Changed exception message in Artifact resolver and fixed logic in keytool test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23989/files
  - new: https://git.openjdk.org/jdk/pull/23989/files/43df6791..83d479cb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23989&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23989&range=00-01

  Stats: 23 lines in 2 files changed: 7 ins; 8 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/23989.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23989/head:pull/23989

PR: https://git.openjdk.org/jdk/pull/23989