Skip non-root user processes when waiting for main proces to end

[robbertvdg]

/kind bug

What steps did you take and what happened:
Metrics cannot be collected while running trials with Istio enabled. The metrics pod keeps running without sending metrics to the db-manager. After debugging I found out that the function GetMainProcesses() waits forever for the Istio sidecar (envoy proxy) to finish. The istio sidecar does not run as root and should therefore be skipped in this proces. The parent process of istio however is the root user (which determines if a process is ran as root). We can check for user id instead of pid parent.

What did you expect to happen:
The istio sidecar should not be considered while checking for the main process to be finished.

Anything else you would like to add:
I will make a PR with a fix.

Environment:

• Kubeflow version 1.0
• Minikube version (minikube version):
• Kubernetes version: (use kubectl version): 1.18.10
• OS (e.g. from /etc/os-release):