cgroup in filesystem.
    
    Move cgroup_t declarations from kernel.te to filesystem.te
    Redo cgroup interfaces in filesystem.if
    Add file context specification for /cgroup mountpoint to filesystem.fc
    
    Signed-off-by: Dominick Grift <domg472@gmail.com>
    Signed-off-by: Chris PeBenito <cpebenito@tresys.com>