commit code coverage for video encoder libmix

BZ:62190

btest is special developed for code coverage tesing toward to libintelmetadatabuffer.
mix_encoder is special developed for code coverage test toward to libmix.
Commit them to mainline branch to keep.
Adjusting code style.
Signed-off-by: Liu Bolun <bolunx.liu@intel.com>

Change-Id: Iecc22aec29ea5e84747f566a55fd2a7f3a1a1677
Reviewed-on: http://android.intel.com:8080/70007
Reviewed-by: Liu, BolunX <bolunx.liu@intel.com>
Reviewed-by: Shi, PingX <pingx.shi@intel.com>
Tested-by: Shi, PingX <pingx.shi@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>
2 files changed