Expose indexing failures statistics using Infinispan indexing failure handler

Indexing operations are done by Hibernate Search on background and by default the Hibernate Search's LogFailureHandler is used to handle possible errors.

We want to use an Infinispan one, capable of collecting the number of failures and we want to expose this information in the IndexStatistics.

This allows us also to drop the use of the failure handler used by the Infinispan tests to check if everything went good on the indexing side.