Index service bugs

The servlet will throw 400 rather than 500 when a task already exists, to
signify that the request has no hope of ever working.

Fix the index task and more docs

Igal druid

Igal druid

QueryResource: Store remote address in user7

Fix request balancing

If the serviceName does not contain ":" this leads to duplicate
registration of firehose with same name

Igal druid

Approximate TopN Query