apd cache directory in /tmp is not unique to user and sometimes causes permissions errors

$ apd-list-pfns Charm EMTF_CharmProductionXSec 
PermissionError: [Errno 13] Permission denied: 
'/tmp/apd_cache/charm/emtf_charmproductionxsec_cacheinfo.json<removed: probably a private token>'

In this case the tmpdir was created by another user on that shared machine and not cleaned up, it is also write protected so cannot be accessed by apd when run by the other user.

the tmp dir should be unique to the current user to avoid this issue. Perhaps this is actually more an issue with how that shared machine is configured.

cc @peilian