In the current implementation these commands are coupled with the
Lucene index. Since at this point Lucene is the only supported
secondary index, this is not a problem. However, if we add support
for a new index type, for example Elasticsearch, this will cause
dependency issues.
A long term solution for this would be to refactor the commands
out of the Lucene implementation into the abstract index API, so
that they can also be used by other index implementations.
For now, as a short term solution, only bind the commands when the
index type is Lucene.
Change-Id: If1e20e656f03ed3cb82a146c669a4105af12c762
9dc12ef0fb