validate maxdelay for cron job

The parameter descriptions says the value should be a positive integer
(or 0). Validate the given value to reject invalid values such as
strings or even negative values.

Change-Id: Ib0937e1c3f6f97959b59e2c5812e3dfe696b6dba

manifests/cron/archive_deleted_rows.pp

@@ -108,7 +108,7 @@ class nova::cron::archive_deleted_rows (
   Boolean $task_log                 = false,
   $sleep                            = undef,
   Boolean $verbose                  = false,
-  $maxdelay                         = 0,
+  Integer[0] $maxdelay              = 0,
   Enum['present', 'absent'] $ensure = 'present',
 ) inherits nova::params {
 

manifests/cron/purge_shadow_tables.pp

@@ -76,7 +76,7 @@ class nova::cron::purge_shadow_tables (
   $age                              = 14,
   Boolean $all_cells                = false,
   Boolean $verbose                  = false,
-  $maxdelay                         = 0,
+  Integer[0] $maxdelay              = 0,
   Enum['present', 'absent'] $ensure = 'present',
 ) inherits nova::params {