ZOOKEEPER-4199: Avoid thread leak in QuorumRequestPipelineTest

`QuorumRequestPipelineTest` hosts parameterized tests which explicitly call `QuorumBase.setUp(boolean)`.

This patch overrides the argument-less `QuorumBase.setUp()` with an empty body, as the former is annotated `BeforeEach`-otherwise causing the runtime to start a fresh 5-ensemble before each test.

Without the override, one such extraneous ensemble is created and immediately leaked for each combination of test method + parameters.

The test consequently requires 4000+ simultaneous threads to complete, and while Linux happily handles that load, macOS Catalina's per-process limit of 2048 threads effectively causes the JVM to "crash" or lock up.

The solution is copied verbatim from another parameterized subclass of `QuorumBase`, `EagerACLFilterTest`.

Author: Damien Diederen <[email protected]>

Reviewers: Enrico Olivelli <[email protected]>, Mate Szalay-Beko <[email protected]>

Closes apache#1591 from ztzg/ZOOKEEPER-4199-thread-leak-qrp-test

zookeeper-server/src/test/java/org/apache/zookeeper/server/quorum/QuorumRequestPipelineTest.java

@@ -36,6 +36,7 @@
 import org.apache.zookeeper.server.quorum.QuorumPeer.ServerState;
 import org.apache.zookeeper.test.QuorumBase;
 import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
@@ -59,6 +60,13 @@ public static Stream<Arguments> data() throws Exception {
                 Arguments.of(ServerState.OBSERVING));
     }
 
+    @BeforeEach
+    @Override
+    public void setUp() {
+        //since parameterized test methods need a parameterized setUp method
+        //the inherited method has to be overridden with an empty function body
+    }
+
     public void setUp(ServerState serverState) throws Exception {
         CountdownWatcher clientWatch = new CountdownWatcher();
         super.setUp(true);