RFR: 2064: Create jsonLocalStorage and htmlLocalStorage in separate directories

[Zhao Song]

In [SKARA-2063](https://bugs.openjdk.org/browse/SKARA-2063), I tried to let WebrevStorage to use HostedRepositoryPool, but I made a mistake. When the bot is trying to create a local clone, it will try to create jsonLocalStorage and htmlLocalStorage in the same directory. And previously, the bot will only create jsonLocalStorage when generateJson is true and create htmlLocalStorage when generateHtml is true. Now, the bot will create both clones when webrevGenerator.generate is called.

To solve this problem, I think the bot should create jsonLocalStorage and htmlLocalStorage in separate directories and the bot should only create the local clone when it's necessary.

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Commit messages:
 - SKARA-2064

Changes: https://git.openjdk.org/skara/pull/1570/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1570&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2064
  Stats: 27 lines in 3 files changed: 8 ins; 1 del; 18 mod
  Patch: https://git.openjdk.org/skara/pull/1570.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1570/head:pull/1570

PR: https://git.openjdk.org/skara/pull/1570