Context directory needs to be configurable

[jason120au]

Currently when using the plan to install PE on a server it copies the installation files to /tmp by default and it appears that at this time this is not configurable. This is a bad idea as many installs have the /tmp directory configured as a separate partition with no exec in the /etc/fstab . Having the context directory configurable aids security posture.

If I modify the params file and add a uploaddr and stagingdir still results in the precheck failing as it seems to copy the precheck.sh to /tmp meaning the installation fails when the /tmp mount settings and permissions are unchanged.