erasure-code: HTML display of benchmark results

erasure-code: HTML display of benchmark results

The ceph_erasure_code_benchmark output is converted into a JSON series
suitable to display in HTML with the http://www.flotcharts.org/
library. A self contained copy of the HTML,JS,CSS files is included for
durability and can be used from the source tree with:

    CEPH_ERASURE_CODE_BENCHMARK=src/ceph_erasure_code_benchmark  \
    PLUGIN_DIRECTORY=src/.libs \
        qa/workunits/erasure-code/bench.sh fplot jerasure |
        tee qa/workunits/erasure-code/bench.js

and display with:

    firefox qa/workunits/erasure-code/bench.html

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