ocfs2: Create stack glue sysfs files.

Introduce a set of sysfs files that describe the current stack glue
state.  The files live under /sys/fs/ocfs2.  The locking_protocol file
displays the version of ocfs2's locking code.  The
loaded_cluster_plugins file displays all of the currently loaded stack
plugins.  When filesystems are mounted, the active_cluster_plugin file
will display the plugin in use.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>