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

[Daniel Fuchs]

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.

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

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

Changes: https://git.openjdk.java.net/jdk/pull/4465/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4465&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268555
  Stats: 304 lines in 10 files changed: 276 ins; 0 del; 28 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4465.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4465/head:pull/4465

PR: https://git.openjdk.java.net/jdk/pull/4465