wrong assumptions in test cases about lock tokens

Several test cases assume that Lock.getLockToken has to return null for locks not attached to the current session. However, this is optional. Citing the Javadoc for getLockToken:

• May return the lock token for this lock. If this lock is open-scoped and
• the current session either holds the lock token for this lock, or the
• repository chooses to expose the lock token to the current session, then
• this method will return that lock token. Otherwise this method will
• return <code>null</code>.