mkfs.gfs2: Allow longer cluster names
    
    Increase the enforced limit for cluster name to 32 bytes and file
    system name to 30 bytes for mkfs.gfs2 (was previously 16 + 16
    bytes).
    
    Also increased this limit in tunegfs2 when labelling gfs2 file
    systems.
    
    Updated the formation in the man pages along with adding a new test
    case for mkfs.gfs2 to validate the increased cluster/file system
    name support.
    
    Resolves: rhbz#1202831
    Signed-off-by: Paul Evans <pevans@redhat.com>