ZOOKEEPER-4232: Run InvalidSnapshotTest on a copy of test data

Without this, the ZooKeeperServer "fixes" the 'snapshot.83f' reference
file, which:

 1. Makes the test ineffective after the first run;
 2. Causes the file to show as modified in version control tools;
 3. Can end up committed by accident.

This patch creates a temporary copy of the data directory.

zookeeper-server/src/test/java/org/apache/zookeeper/test/InvalidSnapshotTest.java

@@ -21,6 +21,7 @@
 import static org.apache.zookeeper.test.ClientBase.CONNECTION_TIMEOUT;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import java.io.File;
+import org.apache.commons.io.FileUtils;
 import org.apache.zookeeper.PortAssignment;
 import org.apache.zookeeper.ZKTestCase;
 import org.apache.zookeeper.ZooKeeper;
@@ -67,7 +68,12 @@ public void testSnapshotFormatterWithNull() throws Exception {
      */
     @Test
     public void testSnapshot() throws Exception {
-        File snapDir = new File(testData, "invalidsnap");
+        File origSnapDir = new File(testData, "invalidsnap");
+
+        // This test otherwise updates the resources directory.
+        File snapDir = ClientBase.createTmpDir();
+        FileUtils.copyDirectory(origSnapDir, snapDir);
+
         ZooKeeperServer zks = new ZooKeeperServer(snapDir, snapDir, 3000);
         SyncRequestProcessor.setSnapCount(1000);
         final int PORT = Integer.parseInt(HOSTPORT.split(":")[1]);