ErasureCodeJerasure: define technique Liber8tion

ErasureCodeJerasure: define technique Liber8tion

technique == "liber8tion"

       ErasureCodeInterface (abstract)
       |
       -> ErasureCodeJerasure (abstract)
          |
          -> ErasureCodeJerasureLiberation
             |
             -> ErasureCodeJerasureLiber8tion
                | == liber8tion

Derived from Liberation it overloads the parse and prepare methods.

parse : default to K=2 and packetsize = 8.
If any of the following constraints is not satisfied, revert to the
default:

  * K <= 8
  * packetsize must not be zero

prepare uses liber8tion_coding_bitmatrix

https://github.com/dachary/ceph/tree/wip-5879 refs #5879

Signed-off-by: Loic Dachary <loic@dachary.org>