Add Dockerfile
Export weight.
Add -haproxy.timeout flag

This flag specifies the timeout when scraping the haproxy stats
endpoint.
Fix: Actually use the newly introduced http.client
Set Deadline for http client

Without a deadline, if the request to haproxy succees but the connection
gets stale, the exporter becomes stale as well.
Update Go download path and enable curl redirects.
Update go from 1.2.1 to 1.4