RFR: 8285878: [TestBug] LocalStorageTest and UserDataDirectoryTest don't always cleanup data dirs [v3]

[Jay Bhaskar]

> Issue: "LocalStorageTest and UserDataDirectoryTest don't always cleanup data dirs"
> Solution:
> 1. All data directories must only be created under the "build" dir. In addition to being a best practice, at least they will be cleaned up by "gradle clean"
> 2. There should be an @AfterClass method that deletes the data dirs
> 3. There should be an @BeforeClass method that also deletes the data dirs prior to running the tests in case it wasn't cleaned up previously

Jay Bhaskar has updated the pull request incrementally with one additional commit since the last revision:

  move webEngine.setUserDataDirectory(null) to after jnunit

-------------

Changes:
  - all: https://git.openjdk.org/jfx/pull/1100/files
  - new: https://git.openjdk.org/jfx/pull/1100/files/c42143f1..ee86247a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1100&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1100&range=01-02

  Stats: 8 lines in 1 file changed: 7 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1100.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1100/head:pull/1100

PR: https://git.openjdk.org/jfx/pull/1100