Setup storage pipeline in the boostrap instead of driver base

This patch moves pipeline setup into the bootstrap and out of
the storage driver base class, so that the base class can be
inherited by meta-drivers, such as the planned sharding manager,
without introducing a loop in the bootstrapping logic.

Now, a meta-driver is exposed to the transport object that
takes care of wiring up the pipeline for each resource
controller behind the scenes.

As part of this work, the pipeline config was modified to
support configuring different stages depending on the
resource. We create three instances of Pipeline anyway,
so it seemed to make sense to allow the operator to
configure the pipelines independently.

Partially-Implements: blueprint storage-pipeline
Change-Id: Ibdb7d0e9537b1eec38a13f4881df7462039bbf98