Add strict validation about boolean parameters

This ensures the parameters used by if-else logic accept only boolean
values because non-boolean can result in unexpected behavior.

Change-Id: I8c2bd97681130da33974e4ea707f77f44e160ce2

manifests/server.pp

@@ -31,6 +31,9 @@ class zaqar::server(
   include zaqar::params
   include zaqar::policy
 
+  validate_legacy(Boolean, 'validate_bool', $manage_service)
+  validate_legacy(Boolean, 'validate_bool', $enabled)
+
   if $manage_service {
     if $enabled {
       $ensure = 'running'

manifests/server_instance.pp

@@ -24,6 +24,8 @@ define zaqar::server_instance(
   include zaqar::deps
   include zaqar::params
 
+  validate_legacy(Boolean, 'validate_bool', $enabled)
+
   if $enabled {
     $service_ensure = 'running'
   } else {