sonobuoy-test-agent: pass '--sonobuoy-image' to 'sonobuoy run'

[etungsten]

Issue number:
Resolves #797

Description of changes:

    sonobuoy-test-agent: pass '--sonobuoy-image' to 'sonobuoy run'
    
    In airgapped testing environments, sonobuoy might not have access to the
    Sonobuoy container image for the worker and aggregator pods.
    
    This lets us configure the source of that image to point to a mirror
    image repo.

Testing done:

sonobuoy-test-agent configuration:

Spec:
  Agent:
    Capabilities:
    Configuration:
      Assume Role:             <nil>
      e2eRepoConfigBase64:   <blah>
      Kube Conformance Image:  123.dkr.ecr.cn-north-1.amazonaws.com.cn/conformance:v1.25.6
      kubeconfigBase64:        ${x86-64-aws-k8s-125.encodedKubeconfig}
      Kubernetes Version:      <nil>
      Mode:                    certified-conformance
      Plugin:                  e2e
      Sonobuoy Image:          123.dkr.ecr.cn-north-1.amazonaws.com.cn/sonobuoy:v0.56.4
    Image:                     123.dkr.ecr.cn-north-1.amazonaws.com.cn/testsys:sonobuoy-test-agent-etung-test
    Keep Running:              false
    Name:                      agent
    Privileged:                <nil>
    Pull Secret:               <nil>
    Secrets:
    Timeout:  <nil>

Checking the sonobuoy pod in the target test cluster, and it shows the expected image:

$ kubectl --kubeconfig ../bottlerocket_release_scripts/shared-testing/cn-x86-64-aws-k8s-125-config describe pod sonobuoy -n sonobuoy
...
Name:         sonobuoy
Namespace:    sonobuoy
Priority:     0
Node:         ip-192-168-78-55.cn-north-1.compute.internal/192.168.78.55
Start Time:   Wed, 29 Mar 2023 00:18:02 +0000
Status:       Running
IP:           192.168.66.124
IPs:
  IP:  192.168.66.124
Containers:
  kube-sonobuoy:
    Container ID:  containerd://dd4b0de1a1bfbf973da29086e64b0f67e4ea930422b252e2aa0c19b2a3b07799
    Image:         123.dkr.ecr.cn-north-1.amazonaws.com.cn/sonobuoy:v0.56.4
    Image ID:      123.dkr.ecr.cn-north-1.amazonaws.com.cn/sonobuoy@sha256:be5e6a32469df1409c647c2a45b6bb1da40d67af1a49175c10928f0b62f161b3
    Port:          <none>
    Host Port:     <none>
..

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[ecpullen]

LGTM