http: changed some var keywords to const and let keywords
_http_agent.js: var keywords changed to const and let keywords. _http_client.js: var keywords changed to const and let keywords.
Changed some var keywords to be const or let keywords to adjust to the ES6 standard ( i did not change var on the loops blocks cause the linter remarks those)
Checklist
- [x ]
make -j4 test
(UNIX), orvcbuild test
(Windows) passes