vfs_glusterfs: Samba VFS module for glusterfs

Implement a Samba VFS plugin for glusterfs based on gluster's gfapi.
This is a "bottom" vfs plugin (not something to be stacked on top of
another module), and translates (most) calls into closest actions
on gfapi.

Signed-off-by: Anand Avati <avati@redhat.com>