using owner/group name for postgresql logs

CHANGELOG.md

 Upcoming version:
 -----------------
+  - using owner/group name for postgresql logs (Nikolaus Krismer)
   - changed hostname retrieval function (Nikolaus Krismer)
   - choosing vagrant provider depending on host (in gradle; not only in vagrantfile) (Nikolaus Krismer)
   - not validating vagrant installation in gradle anymore (Nikolaus Krismer)

Vagrantfile

@@ -87,7 +87,7 @@ Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
   config.vm.synced_folder "conf", "/setup/conf"
   config.vm.synced_folder "data", "/opt/data", create: true
   config.vm.synced_folder "img", "/setup/img"
-  config.vm.synced_folder "log/postgresql", "/var/log/postgresql", create: true, owner: 26, group: 26
+  config.vm.synced_folder "log/postgresql", "/var/log/postgresql", create: true, owner: "postgres", group: "postgres"
   config.vm.synced_folder "log/bootstrap", "/var/log/vagrant_bootstrap", create: true, owner: "vagrant", group: "vagrant"
 
   # Setup environment on startup (done using a shell script)