Added prefix suggestions based on AnalyzingSuggester

This commit introduces near realtime suggestions. For more information about
its usage refer to github issue #3376

From the implementation point of view, a custom AnalyzingSuggester is used
in combination with a custom postingsformat (which is not exposed to the user
anywhere for him to use).

Closes #3376
Improving test CompletionSuggestSearch test stability

Ensuring that the maximum number of replicas is less than the number of nodes.