MB-20497: Clear out the HTTP proxy environment variable.
MB-20497: Clear out the HTTP proxy environment variable.

If the http_proxy and https_proxy environment variables are set
then the golang modules used by Couchbase would honor them and
this can lead to unexpected behavior. Hence clear these variables
in ns_server so that none of the child processes spawned will see
them.

Change-Id: Idee6e206132743d7650b3edfd8f9ebdb536775c0
Reviewed-on: http://review.couchbase.org/67009
Reviewed-by: Aliaksey Artamonau <3c875bcfb3adf2a65b2ae7686ca921e6c9433147@gmail.com>
Tested-by: Ajit Yagaty <670a5cadfa9668cb910cc315f6527868cd5ab42a@couchbase.com>

membase/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,ceejatec/ns_server