Comments out the node_keys_indexable setting if node_indexes are disable...

...d

In the previous pull request that added attributes for node_indexing, the default list of node_keys_indexable was set to the empty string. However, with Neo4j 2.0.0-M03, I am getting the following error when not using node auto indexing: 

SEVERE: Bad value '' for setting 'node_keys_indexable': Must be a comma-separated list of keys to be indexed 

This patch will comment out thenode_keys_indexable property when node_auto_indexing is not enabled.