Bulk functions not work as expected with more than 1 goroutines

[alexisvisco]

As referenced in the issue #9 the bulk function are stuck when using multiple goroutines.

The reason why I have created a bulk function is to dispatch work among multiple goroutines. If this goal is subject to unexpected behavior this code should be refactored to work properly.

[alexisvisco]

An idea is to give access to a pool of connection by default.

Currently the driver use one connections per instance of Ingester/Search... So this is impossible to execute the Push function across multiple goroutines for the same instance.

If an instance have a pool of connections: that will solve the above problem. In addition all bulk functions would be trivial to implement.

[alexisvisco]

Implementing a pool like that https://github.com/fatih/pool should be sufficient for all usages.
Maybe adding an dynamic increase/decrease of the number of available connections.