rgw: switch mongoose to civetweb

Fixes: #7054
mongoose is now GPL, using the civetweb fork instead.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
civetweb: update submodule

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
civetweb: fix module uri

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: modify the civetweb rule

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
civetweb: add include to makefile

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
civetweb: md5.inl -> md5.h

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
mongoose: git rm src/mongoose

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
Merge pull request #1102 from ceph/wip-rgw-civetweb-2

Wip rgw civetweb 2

Reviewed-by: Sage Weil <sage@inktank.com>