Add "can create cronjobs" to linkerd check (#3133)

PR #3056 introduced a cluster heartbeat cronjob to the Linkerd
installation. This implies the user installing Linkerd requires the
privileges to create CronJobs.

Update `linkerd check` to validate the user has privileges necessary to
create CronJobs.

Fixes #3057

Signed-off-by: Andrew Seigner <siggy@buoyant.io>

pkg/healthcheck/healthcheck.go

@@ -387,6 +387,13 @@ func (hc *HealthChecker) allCategories() []category {
 						return hc.checkCanCreate(hc.ControlPlaneNamespace, "extensions", "v1beta1", "deployments")
 					},
 				},
+				{
+					description: "can create CronJobs",
+					hintAnchor:  "pre-k8s",
+					check: func(context.Context) error {
+						return hc.checkCanCreate(hc.ControlPlaneNamespace, "batch", "v1beta1", "cronjobs")
+					},
+				},
 				{
 					description: "can create ConfigMaps",
 					hintAnchor:  "pre-k8s",

test/testdata/check.pre.golden

@@ -19,6 +19,7 @@ pre-kubernetes-setup
 √ can create ServiceAccounts
 √ can create Services
 √ can create Deployments
+√ can create CronJobs
 √ can create ConfigMaps
 √ no clock skew detected