Fix unit tests failure

On current 1.0 branch (and on my machine: Linux), I have the following unit test failures:

• CliTest and EmbeddedCassandraTest: they both first kind of pass (JUnit first prints a message with no failures in it), then hang until JUnit timeout and fails with a 'Timeout occurred'. In other word, the tests themselves are passing, but something they do prevents the process to exit cleanly leading to a JUnit timeout. I don't want to discard that as not a problem, because if something can make the process not exit cleanly, this can be a pain for restarts (and in particular upgrades) and hence would be basically a regression. I'm marking the ticket as blocker (for the release of 1.0.7) mostly because of this one.
• SystemTableTest: throws an assertionError. I haven't checked yet, so that could be an easy one to fix.
• RemoveTest: it fails, saying that '/127.0.0.1:7010 is in use by another process' (consistently). But I have no other process running on port 7010. It's likely just of problem of the test, but it's new and in the meantime removes are not tested.
• I also see a bunch of stack trace with errors like:

      [junit] ERROR 10:01:59,007 Fatal exception in thread Thread[NonPeriodicTasks:1,5,main]
      [junit] java.lang.RuntimeException: java.io.IOException: Unable to create hard link from build/test/cassandra/data/Keyspace1/Indexed1-hc-1-Index.db to /home/mcmanus/Git/cassandra/build/test/cassandra/data/Keyspace1/backups/Indexed1-hc-1-Index.db (errno 17)
  

  (with SSTableReaderTest). This does not make the tests fail, but it is still worth investigating. It may be due to CASSANDRA-3101.