Libreoffice config folder needs to be set

In order to avoid conflicts between multiple instances installed on one server, it's required to define a LibreOffice configuration folder per instance.

Just like with my PR for the documents app (https://github.com/owncloud/documents/pull/353), I propose to use /tmp/owncloud-instanceid
env:UserInstallation was already there in master

My changes were made against stable7 and I merged them to the file in master, so this version is now the properly merged file for master.
I'm just adding `owncloud-<instanceid>` to the path where temp files are stored.
Merge pull request #10827 from oparoz/patch-2

Libreoffice config folder needs to be set