add an EventReceiverFirehoseMonitor so that we can monitor how many
events have been queued in the EventReceiverFirehose and get a sense
about whether the firehose is under too much pressure.
1) Remove maven client from downloading extensions at runtime.
2) Provide a way to load Druid extensions and hadoop dependencies through file system.
3) Refactor pull-deps so that it can download extensions into extension directories.
4) Add documents on how to use this new extension loading mechanism.
5) Change the way how Druid tarball is generated. Now all the extensions + hadoop-client 2.3.0
are packaged within the Druid tarball.
which could cause Guice duplicate binding errors.
Add unit test to replicate duplicate extension issue. Update documents. Add an package accessible getter for loadersMap for testing only.
Notice that extensions explicitly specified in druid.extensions.coordinates have a higher priority than ones included in the classpath.
Extension modules that don't have a canonical class name will be ignored.