Cleanup test classes and add Scope support for TestCluster

TestCluster can currently only be used in a globally shared scope.
This commit adds the ability to use the TestCluster in 3 different
scopes per test-suite. The scopes are 'Global', 'Suite' and 'Test'
where the cluster is shared across all tests, across all test methods or
not at all respectivly.
Subclasses of AbstractIntegrationTest (formerly AbstractSharedClusterTest)
can add an annotation if they need a different scope than Global (default):

```
  @ClusterScope(scope=Scope.Suite, numNodes=1)
```
This also allows to specify the number of shared nodes in that TestCluster
that are available when a test starts.

The cleanups in this commit include:

 - s/Elasticsearch/ElasticSearch/g on test classes
 - Move test classes in org.elasticsearch.test