ErasureCodeJerasure: define technique Liberation

ErasureCodeJerasure: define technique Liberation

technique == "liberation"

parse : default to K=7, M=2 and W=7 and packetsize = 8.
If any of the following constraints is not satisfied, revert to the
default:

 * K > W
 * W > 2
 * W is a prime number
 * packetsize must not be zero
 * packetsize must be a multiple of sizeof(int)

pad_in_length : pad to a multiple of k*w*packetsize*sizeof(int)

prepare, jerasure_encode, jerasure_decode map directly to the matching
jerasure functions

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

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