RFR: 8288885: Introduce a jwebserver launcher utility in test library for jtreg tests

[Jaikiran Pai]

Can I please get a review for this change which adds a utility to the JDK test library to help launch the JWebServer? As noted in the JBS issue, this utility does the necessary work to make sure when the `launch()` method returns, the jwebserver is ready to receive requests. This helps remove a lot of boilerplate code from individual tests.

As part of this commit, the existing `MaxRequestTimeTest` has been migrated to use this new utility. This existing test continues to pass with this change.

tier1, tier2 and tier3 testing passed without any related issues.

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Commit messages:
 - 8288885: Introduce a jwebserver launcher utility in test library for jtreg tests

Changes: https://git.openjdk.org/jdk/pull/9232/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9232&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288885
  Stats: 228 lines in 2 files changed: 170 ins; 38 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/9232.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9232/head:pull/9232

PR: https://git.openjdk.org/jdk/pull/9232