Use /var/tmp for the cached appliance (for FHS compliance).

Use /var/tmp for the cached appliance (for FHS compliance).

The FHS advises large files not to be stored in the root
filesystem[1], and that /var/tmp is persistent across reboots[2]
(whereas /tmp is possibly not[3]).

Therefore we should store the large cached supermin appliance in
/var/tmp instead of /tmp.  /tmp is still used for all other temporary
files and directories.

In either case you can override this by setting $TMPDIR.

[1] http://www.pathname.com/fhs/pub/fhs-2.3.html#THEROOTFILESYSTEM
[2] http://www.pathname.com/fhs/pub/fhs-2.3.html#VARTMPTEMPORARYFILESPRESERVEDBETWEE
[3] http://www.pathname.com/fhs/pub/fhs-2.3.html#TMPTEMPORARYFILES