indexer: Use system config to obtain necessary constants

Cleaned up indexer by removing all hardcoded configurable
values such as ports, num vbuckets, etc. Indexer will now
use only config values passed through system config with
keys having prefix `indexer.`.

Change-Id: I4aa78d5ef62b971eee87e59b5c93717051052dfd
Reviewed-on: http://review.couchbase.org/44081
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>