Run the jaeger-agent as a non-root user by default

[chgl]

Requirement - what kind of business use case are you trying to solve?

I am trying to run the jaeger-agent container in a Kubernetes cluster with strict Pod Security Policies set, which requires all containers to run as non-root users.

Problem - what in Jaeger blocks you from solving the requirement?

The Jaeger-agent container runs as root by default (https://github.com/jaegertracing/jaeger/blob/master/cmd/agent/Dockerfile).

Proposal - what do you suggest to solve the problem or improve the existing situation?

Update the Dockerfile to explicitely set a non-root USER. There's also some open discussion about this over at the Helm chart repo: jaegertracing/helm-charts#41

I would suggest adding a USER directive to the end of the Dockerfile, setting the running user id to 10001. I can create a PR for this.

Any open questions to address

• Should a different UID be used by default? - I prefer 10001 to 1001 suggested in [jaeger] Decide and implement default security context helm-charts#41 as the latter UID is often already used by some account on the host machine.