RFR: 8318662: Refactor some jdk/java/net/httpclient/http2 tests to JUnit

[Mahendra Chhipa]

Refactoring following httpclient/http2 testng test to JUnit :
test/jdk/java/net/httpclient/http2/BadHeadersTest.java
test/jdk/java/net/httpclient/http2/BadPushPromiseTest.java
test/jdk/java/net/httpclient/http2/BasicTest.java
test/jdk/java/net/httpclient/http2/ConnectionFlowControlTest.java
test/jdk/java/net/httpclient/http2/ContinuationFrameTest.java

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Commit messages:
 - JDK-8318662: Refactor some jdk/java/net/httpclient/http2 tests to JUnit

Changes: https://git.openjdk.org/jdk/pull/27388/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27388&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318662
  Stats: 167 lines in 5 files changed: 13 ins; 30 del; 124 mod
  Patch: https://git.openjdk.org/jdk/pull/27388.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27388/head:pull/27388

PR: https://git.openjdk.org/jdk/pull/27388