Ensure ServerSockets are closed in ensureComplete

[xcx1r3]

Description

Any exception occurring before both close() calls complete successfully can lead to one or both ServerSocket instances (and the system ports they hold) not being released.
The best way to fix this is to use the try-with-resources statement, which guarantees that Closeable resources are closed, even if exceptions occur.

int quorumPort;
int electionPort;

 // Use try-with-resources to find available ports and ensure sockets are closed
try (ServerSocket randomSocket1 = new ServerSocket(0);
     ServerSocket randomSocket2 = new ServerSocket(0)) {
     quorumPort = randomSocket1.getLocalPort();
     electionPort = randomSocket2.getLocalPort();
}

[zeekling]

we need an issue in https://issues.apache.org/jira/projects/ZOOKEEPER/summary

[xcx1r3]

I created an issue on https://issues.apache.org/jira/browse/ZOOKEEPER-4935.
Additionally, I discovered other resource leaks, which I have also documented in the same JIRA issue.