Fix lxc_fix_uid script

Actually use predefined variables.

Change-Id: Ifd61bdec98e24f30a1d1b64606c470b7bd84dc69
Merge commit 'refs/changes/88/688/2' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  Fix lxc_fix_uid script

Change-Id: Ie307a0ea7e1de7b08754df8f469f1e7faea6b19b
This is Tuleap 6.3.99.2

Change-Id: Ife93b5f5e77f031417288e6ed5c1c7480d876967