mkfs.gfs2: Fix resource group alignment issue
    
    Make sure the resource groups created when allocating the journals have
    an aligned length to avoid subsequent resource groups start addresses
    getting misaligned. This can cause read-modify-write issues during mkfs
    and likely in other situations, harming performance.
    
    Test case included.
    
    Resolves: rhbz#1440269
    
    Signed-off-by: Andrew Price <anprice@redhat.com>