run db-sync with OpenStack users

When db-sync is run by OpenStack CLI tools (i.e. nova-manage), it writes
in /var/log/ with root user.
In the case where we don't use syslog, the service can't start since it
will try to write as non-root user in the log file.

This patch aims to run the commands with OpenStack users.

manifests/orchestration.pp

@@ -146,7 +146,9 @@ class cloud::orchestration(
   # We have to do this only on the primary node of the galera cluster to avoid race condition
   # https://github.com/enovance/puppet-openstack-cloud/issues/156
   exec {'heat_db_sync':
-    command => '/usr/bin/heat-manage --config-file /etc/heat/heat.conf db_sync',
+    command => 'heat-manage --config-file /etc/heat/heat.conf db_sync',
+    path    => '/usr/bin',
+    user    => 'heat',
     unless  => "/usr/bin/mysql heat -h ${heat_db_host} -u ${encoded_user} -p${encoded_password} -e \"show tables\" | /bin/grep Tables"
   }