RFR: Allow a HostedRepositoryPool to refresh the seed from upstream [v2]

[Robin Westberg]

> Add support for periodically refreshing the seed repository used with the HostedRepositoryPool remote repository cache.
> Also allow the refresh to fail (and instead just use the latest cache) which can be used for operations that can
> tolerate a delayed update (for example, determining the project name from the jcheck configuration file which rarely
> changes).

Robin Westberg has updated the pull request incrementally with one additional commit since the last revision:

  Fix failing tests

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Changes:
  - all: https://git.openjdk.java.net/skara/pull/874/files
  - new: https://git.openjdk.java.net/skara/pull/874/files/11b658e2..52f6c1c1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=skara&pr=874&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=skara&pr=874&range=00-01

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/874.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/874/head:pull/874

PR: https://git.openjdk.java.net/skara/pull/874