Turn class methods into instance methods on GlusterFSXattr

Signed-off-by: Matthew Farrellee <matt@redhat.com>
Make the getfattrCmd configurable, via fs.glusterfs.getfattrcmd, in GlusterFSXattr

To use this,
 0. create a setuid program that
  a. takes a filename (with path) as argv[1]
  b. retrieves trusted.glusterfs.pathinfo with getxattr(2)
  c. prints it to stdout via printf("trusted.glusterfs.pathinfo=\"%s\"\n", ...)
 1. provide it as the value to the fs.glusterfs.getfattrcmd property

Signed-off-by: Matthew Farrellee <matt@redhat.com>
Merge pull request #34 from mattf/configurable-getfattrCmd-2

Configurable getfattr cmd, take 2