Socks proxy support #692

Proposal:
Socks proxy support

Current behavior:
The current proxy setup support http proxy, but not socks protocol

Desired behavior:
Ability to set proxy url like:
socks5h://127.0.0.1:1080

Alternatives considered:
Ability to rely on http(s)_proxy / no_proxy env vars

Use case:
The host I use relies on socks proxy to join external networks, and then join influxdb server.