Changed golang package source from debian packaging to 1.2.2 binary tar ...

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.

The container started nicely, but when trying to connect to the logstash container the tls handshake began shouting :
```
2014/07/03 16:00:17.842093 Connecting to x.x.x.x:5043
2014/07/03 16:00:17.842448 Failed to tls handshake with x.x.x.x:5043 tls: either ServerName or InsecureSkipVerify must be specified in the tls.Config
```
You Can check issues such as https://github.com/elasticsearch/logstash-forwarder/pull/217 to see part of the problem.

You'll understand (like I did) that for the TLS to work, currently logstash-forwarder NEEDS goland >1.1 and <1.3 ... therefore 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 ;)