This command can be used to update existing indexers.

To see what indexers currently exist, run:

 hbase-indexer list-indexers

When updating an index, you only need to specify the properties you want to
change.

The processes running for this indexer will be restarted in order to use the
new settings. This happens asynchronously, thus not necessarily before this
tool returns.

For example, if you changed the indexerconf.xml, you would run:

 hbase-indexer update-indexer -n index-name -c indexerconf.xml
