[test] Prevent hard-coded path

The hardcoded path used in this test conflicts with a pre-existing path by another user/process. This commit adds an existence check and a bit of randomness in the directory name.

Fixes SMACK-955

smack-openpgp/src/test/java/org/jivesoftware/smackx/ox/SecretKeyBackupHelperTest.java

@@ -26,6 +26,7 @@
 import java.util.Collections;
 
 import org.jivesoftware.smack.test.util.SmackTestSuite;
+import org.jivesoftware.smack.util.StringUtils;
 
 import org.jivesoftware.smackx.ox.crypto.PainlessOpenPgpProvider;
 import org.jivesoftware.smackx.ox.element.SecretkeyElement;
@@ -51,7 +52,11 @@ public class SecretKeyBackupHelperTest extends SmackTestSuite {
     private static final File basePath;
 
     static {
-        basePath = new File(org.apache.commons.io.FileUtils.getTempDirectory(), "ox_secret_keys");
+        File path;
+        do {
+            path = new File(org.apache.commons.io.FileUtils.getTempDirectory(), "ox_secret_keys_" + StringUtils.randomString(3));
+        } while (path.exists());
+        basePath = path;
     }
 
     @Test