Improve security-scan's debugging/logging

[andypitcher]

The creation of custom CIS benchmarks in Rancher can lead to failing security-scan pod. Scans will stay in running or pending state, without any further indication or logs.

When this failure happens, the security-scan pod gets removed right away without providing any logs. This is likely related to kube-bench's failure to execute a given custom benchmark.

This issue is to improve the following:

1. Add some tests around the created CIS benchmarks (same as kube-bench and yamlint tests)
2. Improve logging/debugging of kube-bench in run_sonobuoy_plugin.sh
3. Do not remove security-scan's pod on failure, so that user can dump the logs and investigate