Add kube-bench dry run to script/validate

[andypitcher]

Parent issue: rancher/cis-operator#227

This PR adds another layer of verification, to ensure that a given CIS benchmark is not faulty.

Let's say we introduce a typo in cis-1.7/master.yaml, (tiype instead of type), but yamllint didn't return any errors. Kube-bench can be run against the given benchmark (e.g cis-1.7), if any of the cis-1.7's files have a typo it won't run.
kube-bench indicates which component (file) is faulty : error setting up master controls: non-master controls file specified

Example of scenario:

$ git diff
diff --git a/package/cfg/cis-1.7/master.yaml b/package/cfg/cis-1.7/master.yaml
index aa27cb4..647a813 100644
--- a/package/cfg/cis-1.7/master.yaml
+++ b/package/cfg/cis-1.7/master.yaml
@@ -3,7 +3,7 @@ controls:
 version: "1.7"
 id: 1
 text: "Control Plane Security Configuration"
-type: "master"
+type: "master"
 groups:
   - id: 1.1
     text: "Control Plane Node Configuration Files"

YAMLLINT test 🟢

$ yamllint security-scan/package/cfg/cis-1.7/master.yaml | grep -v line
security-scan/package/cfg/cis-1.7/master.yaml

KUBE-BENCH dry-run 🔴

$ ./kube-bench --config-dir security-scan/package/cfg --config security-scan/package/cfg/config.yaml --benchmark cis-1.7
Warning: Kubernetes version was not auto-detected because kubectl could not connect to the Kubernetes server. This may be because the kubeconfig information is missing or has credentials that do not match the server. Assuming default version 1.18

error setting up master controls: non-master controls file specified

[rayandas]

@andypitcher can you please rebase it?

[rayandas]

lgtm