Improve websocket test execution time

Tests under jdk/java/net/httpclient/websocket take a long time to execute.
The entire directory is marked as exclusive [1], which means that the tests are never executed in parallel.
Tests named Pending*** (e.g. PendingPongBinaryClose) use inflated timeouts to make them more reliable. They can be modified to initially use shorter timeouts, and retry if the timeouts prove to be too short.

[1] https://github.com/openjdk/jdk/blob/master/test/jdk/TEST.ROOT#L29