Specify various volume attributes

GPFS provides a variety of knobs which together define the performance and reliability characteristics of a volume. This BP in particular proposes to specify the following attributes when creating a new volume:

* The storage pool on which the volume is placed
* Number of block-level replicas
* Whether the physical blocks should be allocated locally on the node issuing the IO or striped across the cluster
* Whether writes to the volume should use direct IO
* Number of file system blocks to be laid out sequentially on disk to behave like a single large block
* Local storage attached to specific node(s) where the replicas of the volume should be allocated