Ignore --bootstrap-kubeconfig flag when config file already present

[shivi28]

What steps did you take and what happened:

When we restart byo host agent, and if we passed --bootstrap-kubeconfig flag during the restart, then our controller fails with error message:

This happens because when we pass --bootstrap-kubeconfig flag again, then it generates the new CSR which is validated against old private key, which throws compatibility issue

What did you expect to happen:
To avoid this issue, we should ignore the --bootstrap-kubeconfig flag if config is already present in its path.

Environment:

• Cluster-api-provider-bringyourownhost version:
• Kubernetes version: (use kubectl version --short):
• OS (e.g. from /etc/os-release):