GCP workers should install cloud ops agent

[lotas]

We have sometimes issues with workers/task dying without anything visible in the logs.
Also, memory usage metrics are not available because GCP requires extra agent to be installed on the worker

https://cloud.google.com/stackdriver/docs/solutions/agents/ops-agent/installation

TODO:
Add ops agent install in image building

curl -sSO https://dl.google.com/cloudagents/add-google-cloud-ops-agent-repo.sh
sudo bash add-google-cloud-ops-agent-repo.sh --also-install