Merge pull request #975 from BCLibCoop/bclibcoop/rgw_cors

RGW: CORS use the correct headers for checking, and validate headers as lowercase where needed

Reviewed-by: Yehuda Sadeh <yehuda@inktank.com>

diff --cc src/rgw/rgw_op.cc
Simple merge

diff --cc src/rgw/rgw_rest.cc
Simple merge