RFR: 8266250: WebSocketTest and WebSocketProxyTest call assertEquals(List<byte[]>, List<byte[]>)

[Daniel Fuchs]

Please find here an almost trivial test fix that should improve diagnostic in case of failures. 
It also avoids relying on an unspecified behavior of `Assert.assertEquals`.

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Commit messages:
 - 8266250: WebSocketTest and WebSocketProxyTest call assertEquals(List<byte[]>, List<byte[]>)

Changes: https://git.openjdk.java.net/jdk/pull/3776/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3776&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266250
  Stats: 50 lines in 2 files changed: 48 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3776.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3776/head:pull/3776

PR: https://git.openjdk.java.net/jdk/pull/3776