osd: erasure code benchmark tool

Implement the ceph_erasure_code_benchmark utility to:

* load an erasure code plugin

* loop over the encode/decode function using the parameters from the
  command line

* print the number of bytes encoded/decoded and the time to process

When decoding, random chunks ( as set with --erasures ) are lost on each
run.

For instance:

    $ ceph_erasure_code_benchmark \
       --plugin jerasure \
       --parameter erasure-code-directory=.libs \
       --parameter erasure-code-technique=reed_sol_van \
       --parameter erasure-code-k=2 \
       --parameter erasure-code-m=2 \
       --workload decode \
       --erasures 2 \
       --iterations 1000
    0.964759	1048576

shows 1GB is decoded in 1second.

It is intended to be used by other scripts to present a human readable
output or detect performance regressions.

Signed-off-by: Loic Dachary <loic@dachary.org>
osd: erasure code benchmark workunit

Display benchmark results for the default erasure code plugins, in a tab
separated CSV file. The first two column contain the amount of KB
that were coded or decoded, for a given combination of parameters
displayed in the following fields.

seconds	KB	plugin	k	m	work.	iter.	size	eras.
1.2	10	example	2	1	encode	10	1024	0
0.5	10	example	2	1	decode	10	1024	1

It can be used as input for a human readable report. It is also intented
to be used to show if a given version of an erasure code plugin performs
better than another.

The last column ( not shown above for brievety ) is the exact command
that was run to produce the result so it can be copy / pasted to
reproduce them or to profile.

Only the jerasure techniques mentionned in
https://www.usenix.org/legacy/events/fast09/tech/full_papers/plank/plank_html/
are benchmarked, the others are assumed to be less interesting.

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