[GFS2] Add gfs2meta filesystem

In order to separate out the filesystem's metadata from "normal"
files and directories, a new filesystem type has been created.
It is called gfs2meta and mounting it gives access to the files
that were previously under .gfs2_admin (well still are until mkfs
is altered, which is next on the adgenda).

Its not currently possible to mount both gfs2 and gfs2meta on the
same block device at the same time. A future patch will allow that
to happen.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>