check_rancher2

Use 'command -v' instead of 'which' for required command check. Makes the plugin more distribution independent, as which is not always installed by default - depending on the Linux distribution.

This release adds a new check type to the plugin.

The "local-certs" check type allows to check for valid certificates deployed by Rancher in the "local" cluster, under the "System" project. These certificates are deployed as Kubernetes secrets in the "cattle-system" namespace.

These certificates are by default created with a one year validity (Rancher, whyyyy?!). When these local certificates expire, this can create some issues in the background of Rancher, e.g. when RBAC actions are used. It's therefore important to verify these certificates have not expired.