Add LVM support, and use recommended xfs settings, as per RHS.

* Add LVM support.
* Add optional partitioning.
* Set xfs inode size, for xattr performance.
* Set xfs logical block size for directory performance.
* Set xfs stripe unit size and stripe width for RAID alignment.
Allow specifying brick device and other parameters in gluster::simple.

This patch adds support to specify the brick device values as a hash.