Go Compiler Version .. second round

The last pull request I made did make the docker build work .... however, after building the logstash forwarder did not work (unable to connect to the logstash instance) because of the version of the go compiler Debian provides.

I you check issues such as 
https://github.com/elasticsearch/logstash-forwarder/pull/217
You'll understand (like I did) that for the TLS to work, currently logstash-forwarder NEEDS goland 1.2.x ... however debian does not provide this version anymore ...

So I changed the Dockerfile to download the binary tar.gz of the go 1.2.2 compiler, made a few changes to take this into account and ... there we go ;)

PS : sorry for the useless commits included in this pull request ... It's only my second PR, and well ... I must have failed somewhere ;)