* Added unit-tests for treeWalkPool
* Added unit tests for tree-walk-fs
* Added period at the end of all comments.
* FS/XL: Unified tree walk tests for both backends
* Added disk failure related tests for treewalk
Replaced removeRandomDisks with removeDiskN. There is no need to
randomize disks that fail while the distribution of chunks in XL during
erasure coding data is random.
