RFR: 8288885: Introduce a jwebserver launcher utility in test library for jtreg tests [v2]

[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.

Jaikiran Pai has updated the pull request incrementally with one additional commit since the last revision:

  clarify that the jwebserver is launched as a separate process and needs to be destroyed by the caller when it's no longer needed

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9232/files
  - new: https://git.openjdk.org/jdk/pull/9232/files/f031ab7b..95d6f9c1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9232&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9232&range=00-01

  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 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