gfs2-utils: Move metafs handling into gfs2/mkfs/
    
    gfs2_grow and gfs2_jadd are the two remaining mounters of the metafs so
    move the high-level metafs mounting bits from libgfs2/misc.c into the
    mkfs directory and give them a suitable interface.
    
    This allows the metafs-related fields to be removed from struct gfs2_sbd
    and the metafs_interrupted flag and the signal handling functions
    exported by libgfs2 to be pushed down into the applications.
    
    Signed-off-by: Andrew Price <anprice@redhat.com>