Add windows Dockerfiles for gitlab-runner-helper

What does this MR do?

Add windows dockerfiles for GitLab Runner Helper

Why was this MR needed?

In #3755 (closed) we need to start publishing windows based container images so the helper can be used on windows server

How to test

• Run gox -osarch=windows/amd64 -ldflags "-X gitlab.com/gitlab-org/gitlab-runner/common.NAME=gitlab-runner -X gitlab.com/gitlab-org/gitlab-runner/common.VERSION=11.9.0~beta.1133.g4f3513f0 -X gitlab.com/gitlab-org/gitlab-runner/common.REVISION=4f3513f0 -X gitlab.com/gitlab-org/gitlab-runner/common.BUILT=2019-02-27T09:11:59+0000 -X gitlab.com/gitlab-org/gitlab-runner/common.BRANCH=3755-helper-image-for-windows-container-execution -s -w" -output=dockerfiles/build/binaries/gitlab-runner-helper.x86_64-windows gitlab.com/gitlab-org/gitlab-runner/apps/gitlab-runner-helper to build the binary
• Run vagrant up
• vagrant ssh
• Type in powershell to invoke PowerShell
• cd C:\Go\src\gitlab.com\gitlab-org\gitlab-runner\
• docker build --no-cache -t gitlab/gitlab-runner-helper:windows1809_x86_64-g4f3513f0 -f .\dockerfiles\build\Dockerfile.dockerfiles/build/Dockerfile.x86_64_nanoserver1809 .\dockerfiles\build
• docker run --rm -it gitlab/gitlab-runner-helper:windows1809_x86_64-f6cd0a19 now you should have shell access to the windows container
• dir ".\Program Files"

Are there points in the code the reviewer needs to double check?

• Right now the scripts are not being copied over since they are bash scripts. There are plans to migrate over those bash scripts on to the gitlab-runner-helper.exe itself in #3755 (closed)

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

#3755 (closed)