installscript(s) should not use /tmp

[surfnet-niels]

When installing OpenConext a lot of stuff is dumped into /tmp (e.g. grouper jar). As /tmp is often a small partition, or being shared with e.g. /var and /root as part of the / partition, this quickly fills up the root of a machine, and may even lead to premature ending of the install if the machine runs out of disk space.

As the script is always trying to install to /opt, I propose to create a temporary directry in /opt/tmp to hold these files