RFR: 8298588: WebSockets: HandshakeUrlEncodingTest unnecessarily depends on a response body [v3]

[Michal Karm Babacek]

> According to [rfc6455](https://www.rfc-editor.org/rfc/rfc6455.html#section-5.5.1), the close frame MAY contain a body, i.e. it is considered [optional](https://www.rfc-editor.org/rfc/rfc2119#section-5). It seems that the contemporary JDK HEAD (tip) does populate the body and thus enables `HandshakeUrlEncodingTest.java` to parse its contents. On the contrary, JDK 11 does not populate the body in the same case. I would like to backport JDK-8245245 all the way to JDK 11, so I would like to change the behavior of this test so as it works across JDK versions.

Michal Karm Babacek has updated the pull request incrementally with one additional commit since the last revision:

  Response body is always checked

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11486/files
  - new: https://git.openjdk.org/jdk/pull/11486/files/3ad9c24e..5b6c78bb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11486&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11486&range=01-02

  Stats: 6 lines in 1 file changed: 0 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/11486.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11486/head:pull/11486

PR: https://git.openjdk.org/jdk/pull/11486