[go-server] Add dockerfile for building and run petstore service

[etherealjoy]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

This PR aims to introduce a docker file to build and host the go server generated code inside a container.
Requests can be directed to container using API calls from a client.

• Tested using curl on Linux

@antihax @wing328

[wing328]

cc @bvwells as well

[wing328]

@etherealjoy should petstore be replaced by {{{packageName}}} instead?

[etherealjoy]

indeed, I have updated the commit.

[wing328]

Tested locally and the result is good: (partial result)

Removing intermediate container 1cde8effa6b7
 ---> 3850dc3daa87
Step 11/11 : ENTRYPOINT ["./petstoreserver"]
 ---> Running in 04dc9f79b86d
Removing intermediate container 04dc9f79b86d
 ---> 0cca2b780ae2
Successfully built 0cca2b780ae2
Successfully tagged petstoreserver:latest
➜  go-api-server git:(etherealjoy-go-server_add_dockerfile) ✗ docker run --rm -it petstoreserver 
2018/06/13 08:53:57 Server started