orangefs: Implement show_options

Implement the show_options superblock op for orangefs as part of a bid to
rid of s_options and generic_show_options() to make it easier to implement
a context-based mount where the mount options can be passed individually
over a file descriptor.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Mike Marshall <hubcap@omnibond.com>
cc: pvfs2-developers@beowulf-underground.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>