8268555: Update HttpClient tests that use ITestContext to jtreg 6+1

[dfuch]

Another change brought by jtreg 6+1 in the behavior of @BeforeMethod.
Now throwing an exception in @BeforeMethod causes all annotated methods to be skipped, not just those annotated with @Test.

HttpClient tests that use @BeforeMethod and ITestContext need to be updated to work around the new behavior.

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Issue

• JDK-8268555: Update HttpClient tests that use ITestContext to jtreg 6+1

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[mlbridge]

Webrevs

• 00: Full (4aae472a)

[dfuch]

Closing this PR in favor of one targeted at JDK 17: openjdk/jdk17#5