Forbid concurrent runs of pod pruner

This is a solution to a problem when a pod is stuck. Pod pruner is not
able to remove it and won't finish. After some time, there will be
multiple pod pruners running, all unable to finish. This will result in
using up all the cronjobs resources

Signed-off-by: mkosiarc <mkosiarc@redhat.com>

tasks/configure_namespace.yml

@@ -145,6 +145,7 @@
         name: "{{ item.name }}"
       spec:
         schedule: "{{ pod_pruning_schedule }}"
+        concurrencyPolicy: Forbid
         successfulJobsHistoryLimit: "{{ osbs_generic_cronjob_successful_jobs }}"
         failedJobsHistoryLimit: "{{ osbs_generic_cronjob_failed_jobs }}"
         jobTemplate: