golang net/http package honours HTTP_PROXY / HTTPS_PROXY Environment Variables

Similar to curl/libcurl in MB-15438, the net/http package used by Couchbase's golang modules honours the proxy-related HTTP_PROXY and HTTPS_PROXY environment variables.

This definitely affects the communication between indexer and projector, but can in theory affect any golang module that uses net/http.

There are a few potential issues. If the proxy expects authentication then the indexer will be unable to communicate with the projector. If it doesn't and the communication successfully takes place via the proxy, then we will be potentially transferring a lot of inter-node data via a third-party, probably on a different subnet, which will likely have an effect on performance.

The fix is similar to MB-15438 - making sure the environment is sane before launching the golang module(s) from ns_server's ns_ports_setup.erl. If there's any chance we will use HTTPS as well as HTTP in the future then both variables should be cleared.