Exclude tar.gz and zip files from Runtime archive

[aLekSer]

Fix exponential growth of agonessdk-$(VERSION)-runtime archive caused by adding all files including old version of archives into new archive.
Closes #589.

[agones-bot]

Build Succeeded 👏

Build Id: 8b80bb5a-68c9-4cc9-b7af-7f5114bb5298

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:0.8.0-beb98cb
• image: gcr.io/agones-images/agones-sdk:0.8.0-beb98cb
• image: gcr.io/agones-images/agones-ping:0.8.0-beb98cb
• Linux C++ SDK (build: dev): agonessdk-0.8.0-beb98cb-dev-linux-arch_64.tar.gz
• Linux C++ SDK (build: runtime): agonessdk-0.8.0-beb98cb-runtime-linux-arch_64.tar.gz
• Linux C++ SDK (source): agonessdk-0.8.0-beb98cb-src.zip
• SDK Server: agonessdk-server-0.8.0-beb98cb.zip

A preview of the website (the last 30 builds are retained):

• https://beb98cb-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/596/head:pr_596 && git checkout pr_596
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=0.8.0-beb98cb