Use XORG_LOCK_DIR for Xorg lock files and sockets
The case of firefox 60 described in the commit messages showed that we should not use $TMPDIR instead of /tmp in our patch to isolate $DISPLAYs.
This introduce a new environment variable XORG_LOCK_DIR with clearer semantics.
Softwares relying on this have been updated or removed when not used.
The following softwares where already OK:
- ERP5 and erp5testnode did not set
$TMPDIRand were using/tmp/ - cloudooo runs in
--headlessmode