identity: disable log_file param when using syslog

When using syslog, ensure that log_file is empty to avoid multiple
logging.

Close bug #360

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

manifests/identity.pp

@@ -404,6 +404,9 @@ class cloud::identity (
   # Disable twice logging if syslog is enabled
   if $use_syslog {
     $log_dir = false
+    keystone_config {
+      'DEFAULT/log_file': ensure => absent;
+    }
   } else {
     $log_dir = '/var/log/keystone'
   }

spec/classes/cloud_identity_spec.rb

@@ -115,6 +115,7 @@ describe 'cloud::identity' do
         :log_dir             => false
       )
       should contain_keystone_config('ec2/driver').with('value' => 'keystone.contrib.ec2.backends.sql.Ec2')
+      should contain_keystone_config('DEFAULT/log_file').with_ensure('absent')
     end
 
     it 'checks if Keystone DB is populated' do