lower concurrent parallel tests to 12
lower concurrent parallel tests to 12

We noticed on collectd, that even 16 is sometimes too high

dhoppe/modulesync_config,voxpupuli/modulesync_config,voxpupuli/modulesync_config,dhoppe/modulesync_config,dhoppe/modulesync_config,voxpupuli/modulesync_config,puppet-community/modulesync_config,dhoppe/modulesync_config,voxpupuli/modulesync_config