http: add http transport

This implement basic http transport via fastcgi. All the http operation are
left empty and just return 'unplemented' notice back.

Later if we write specific http handling as for swift or S3 service, we need
just implement GET/PUT/POST/HEAD/DELETE handlers respectively.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>