Refactored parseAttrs

Moved parseAttrs from GlusterFileChannel to GlusterFileAttributes. Made it a static method to enable its use in GFChannel. Modified the unit tests for GFAttributes and GFChannel to reflect this refactoring.
As per our conversation in our meeting this evening...

A triple-nested for loop is a sign of "code smell," which suggests at least that the code should be refactored for readability, or else rearchitected to remove complexity in the design.

We discussed the goals this code was trying to achieve:
- A single statement of the correspondence between a file's integer "mode" value and a set of high level PosixFilePermissions.
- Ability to look up a relation in the correspondence by integer mode and get a set of PosixFilePermissions, or vice versa, just as easily.

Finally, we came up with a more elegant solution that involves:
- A static block in a class, with
- A Map representing the correspondence in one direction, say modeToPermission, and
- A small code block (or static method) which inverts the Map and stores the result, say permissionToMode