Match an exclusion or warning rule when the entry is a partial match

[rgeyer]

While working on an existing mixin, several dashboards have a similar reason for exclusion (shown below), but the linter was not excluding them.

Turns out that because the lint error contained a panel name and target idx, the match was not "exact" and was being skipped.

This PR resolves that, and allows partial matches for specific entries on a rule.

exclusions:
  target-instance-rule:    
    reason: These dashboards are cluster wide dashboards. As such 'cluster' takes the place of 'instance'
    entries:
    - dashboard: Kubernetes / Persistent Volumes
    - dashboard: Kubernetes / Compute Resources /  Multi-Cluster
    - dashboard: Kubernetes / Compute Resources / Node (Pods)

[mem]

LGTM