Remove duplicate registration of service

If the serviceName does not contain ":" this leads to duplicate
registration of firehose with same name
fix connection counting
Add registration for backward compatibility
make server selection configurable, add back random server selection
simplify things a bit
add docs
Merge pull request #353 from metamx/fix-request-balancing

Fix request balancing
add connection count test in case of failure
QueryResource: Store remote address in user7
Merge pull request #354 from metamx/request-peer-metric

QueryResource: Store remote address in user7
final draft
Merge branch 'master' into igalDruid