Now NDB is only initialized and started when the tests that are
  being run will make use of it. The same thing is also done for the
  slave databases and the instance manager.

  After review from Magnus: Only take a snapshot of the data directories
  that are in use.


mysql-test/mysql-test-run.pl:
  Only initialize (and start) NDB, the instance manager, and the slaves
  when we have tests that require them. Also, only snapshot the data
  directories that we are going to use.
mysql-test/ndb/ndbcluster.sh:
  Fix text message that has always annoyed me