Fix restart bugs in ZkCloudnameIntegrationTest.

There were a few bugs related to restarting EmbeddedZooKeeper that caused
ZkCloudnameIntegrationTest to fail on Windows:

- EmbeddedZooKeeper.shutdown() didn't close the transaction log,
  making deletion fail on Windows since the file handle was still open
- EmbeddedZooKeeper.del() didn't verify that files were successfully
  deleted
- ZkCloudNameIntegrationTest.testZookeeperRestart() didn't retry
  coordinate creation if the connection to ZooKeeper failed, leading to a
  race condition when restarting ZooKeeper, as coordinate creation doesn't
  wait for ZooKeeper to get back online

This commit fixes these bugs, allowing the unit test suite to run
successfully on Windows.
Merge pull request #134 from markusbk/zkintegration-winfix

Fix restart bugs in ZkCloudnameIntegrationTest.