java/util/prefs/* tests can't be safely run simultaneously under the same user account
(which is what could happen during automatic (nightly/weekly) testing).

As result different tests can fail.
For example:
1. java/util/prefs/RemoveReadOnlyNode.java can fail with
   "java.util.prefs.BackingStoreException: java.io.FileNotFoundException: /import/gtee/.java/.userPrefs/node1/node1B/prefs.tmp (Permission denied)" exception

2. other tests can fail with "java.util.prefs.BackingStoreException: Couldn't get file lock."

Full list of tests is:
 java/util/prefs/CommentsInXml.java
 java/util/prefs/ConflictInFlush.java
 java/util/prefs/ExportNode.java
 java/util/prefs/ExportSubtree.java
 java/util/prefs/PrefsSpi.sh
 java/util/prefs/RemoveReadOnlyNode.java
 java/util/prefs/RemoveUnregedListener.java
 java/util/prefs/SerializeExceptions.java

It would be good (if possible) to rewrite the tests so they can safely run simultaneously under the same user account.